There is certainly no problem in using a single shared 'jbcore' folder for all your galleries (please see the Using an External jbcore Folder support section for details) and if you are seeing the "Config file not found." message, then the path to your 'juicebox.js' file (within the 'jbcore' folder) is correct.

If you are using a baseUrl, then the baseUrl entry should point towards a complete gallery folder.
The gallery's configuration file should be named 'config.xml' (its default name) and should be located directly within the gallery folder (its default location).
If you change the name of the configuration file or move it, then you can point towards it with a configUrl entry in your gallery's embedding code (please see the Embed Options section of the Config Options page).
However, a configUrl should not be necessary unless you want to manually change the structure of the gallery (or rename the configuration file).

Just make sure that your 'config.xml' files are inside your gallery folders (where they should be if you created your galleries with JuiceboxBuilder-Lite) and that your baseUrl entries point towards your gallery folders.
The baseUrl entries can be relative paths (relative to the web page containing the embedding code) or absolute paths (in the form 'http://www.example.com/gallery_folder/'.

At the moment, your baseUrl entries are relative paths and your 'ValleyForge2017' and 'Germantown201' gallery folders should be located in the same directory as the web page whose HTML code you posted.

After creating your galleries with JuiceboxBuilder-Lite (and saving each one to its own individual folder), there is no need to modify the gallery folders at all.
Just upload them to your web server and make sure that the baseUrl paths are correct.
For reference, the baseUrl method of embedding is documented here.

General information about the "Config file not found." message can be found in this FAQ:
When I view my gallery I see the message 'Config file not found'. How do I fix this?

Incidentally, if you encounter the "Config file not found." message whilst trying to view a gallery locally (from your computer rather than from your web server) in Safari 11, then please see this forum post for a full explanation and a workaround.

Unfortunately, Safari 11 (released 19 September 2017) introduced a new security restriction which prevents local viewing of Juicebox galleries by default. This issue is specific to viewing galleries locally (from your computer's hard drive) and there is no such issue once the galleries have been uploaded to a web server (where they can be viewed in any modern browser).
Selecting 'Disable Local File Restrictions' from Safari 11's 'Develop' menu (full instructions in the link above) should, once again, allow you to view your galleries locally in Safari 11.

I hope this helps.
However, if you continue to experience difficulties, then please post the URL to your web page so that I can take a look at the problem and help further.

I'm gad you've been able to find the answer to your problem.
Thank you for letting me know.

Here's some more information for others reading this forum thread and encountering similar issues.

Your screenshot shows the Splash Page.
The Splash Page is a placeholder for the gallery which is displayed by default on small screen devices when the gallery is embedded in a web page alongside other content (rather than displayed on a page of its own with dimensions of 100% x 100%, filling the browser window) and may may too small to be usable.
The Splash Page is essentially an image link for the gallery which displays an image (by default, the first image in the gallery) and some text.
When the user clicks or taps the Splash Page, the gallery is expanded to fill the browser window (giving the images more space to be displayed).
More information about the Splash Page can be found in the Screen Modes section of the Gallery Tour.

If you want AutoPlay to start once the gallery has been expanded from the Splash Page, set autoPlayOnLoad="TRUE" (in JuiceboxBuilder-Pro's 'Customize -> Autoplay' section) in conjunction with showSmallThumbsOnLoad="FALSE" ('Customize -> Thumbnails').

If you would rather not use the Splash Page, then set showSplashPage="NEVER" ('Customize -> Splash Page').

Alternatively, you could force the gallery to be displayed in Large Screen Mode (which, by default, does not use the Splash Page) on all devices and in all browsers by setting screenMode="LARGE" ('Customize -> General').

For reference, all the Splash Page configuration options can be found here.

The 'juicebox.js' and 'juicebox.php' files do not change from gallery to gallery.
The 'pswd.php' file contains the password for a gallery (if you choose to password-protect it).
Please see the Password Protection support section for details.

If you do not want to password-protect your galleries (or if you are happy to use the same password for all your galleries), then all your galleries can share a single instance of the entire 'jbcore' folder (rather than having an individual 'jbcore' folder for each gallery).
If you'd like to do this, then please see the Using an External jbcore Folder support section for details.

Essentially, all you need to do is upload a single 'jbcore' folder to somewhere on your web server and make sure that the 'juicebox.js file (from within the 'jbcore' folder) is loaded via a <script> tag on every page which contains a gallery.

Thank you for providing the link to your gallery and the contents of your gallery's 'index.html' file.
Your gallery at http://robertjohn.me/wplightbox/test/ seems to be fine (and your gallery's 'index.html' file also seems to be fine).
I have viewed the gallery in Chrome 64, Edge, Firefox 58.0.2, IE11 and Opera 51 and it displays and functions correctly in all browsers.
There seems to be no problem with any of the gallery files on your web server.

Whatever browser you are using to view your gallery, please double-check that you have completely cleared its cache before reloading the gallery's web page.
Also, check to see if you have any browser extensions installed which may somehow be interfering with the gallery (and try temporarily disabling them to see if this helps).

If you encounter the "Config file not found." message whilst trying to view a gallery locally (from your computer rather than from your web server) in Safari 11, then please see this forum post for a full explanation and a workaround.

Unfortunately, Safari 11 (released 19 September 2017) introduced a new security restriction which prevents local viewing of Juicebox galleries by default. This issue is specific to viewing galleries locally (from your computer's hard drive) and there is no such issue once the galleries have been uploaded to a web server (where they can be viewed in any modern browser).
Selecting 'Disable Local File Restrictions' from Safari 11's 'Develop' menu (full instructions in the link above) should, once again, allow you to view your galleries locally in Safari 11.

More general information on the "Config file not found." message can be found in this FAQ:
When I view my gallery I see the message 'Config file not found'. How do I fix this?

However, there seems to be no problem with your 'test' gallery online and ensuring that your browser's cache has been cleared before reloading the gallery's web page and making sure that you have no browser extensions enabled which may be interfering with the gallery should hopefully help.

Please let me know how you get on.

You're welcome.
I hope you get on OK.
If you get stuck with anything or if I can be of any further assistance, please let me know.

You could always embed the information within your images as IPTC data (using a program such as Lightroom or Photoshop) so that, no matter what the images are named, the information always travels with the images wherever they go (and can be read by most imaging programs).

JuiceboxBuilder-Lite can also extract IPTC data from images for use as the image titles (IPTC Document Title) and image captions (IPTC Description) via the 'Images -> Titles -> Use IPTC Title' and 'Images -> Captions -> Use IPTC Captions' options from the drop-down menu at the top.

However, please be aware that when JuiceboxBuilder-Lite resizes images, all metadata is removed for the resulting gallery images so, if you have IPTC data within your images and want this data to remain in the gallery images, then resize your images in an imaging program first, prior to feeding them to JuiceboxBuilder-Lite, and deselect the 'Resize Images' checkbox on the 'Images' tab (so that JuiceboxBuilder-Lite does not process the images further).

You're welcome.
I'll mark this thread as 'solved' but if you have any further trouble, just post back here and I'll do my best to help you out.

It certainly sounds like there might be a problem with certain images and, when JuiceboxBuilder-Lite chokes on them, the publishing process grinds to a halt, resulting in an incomplete gallery folder.
If you could upload the images that you are having trouble with (so that I can download them and use them in a test gallery), I'll certainly take a look to see if I can replicate the issue (and maybe find the root of the problem).

It seems very strange that you have re-saved the image in different formats and JuiceboxBuilder-Lite rejects them all.
Normally, if an image is corrupt, the best thing to do is find an imaging program that can open it and then just re-save it (without making any changes to it). The process of re-saving the image can sometimes fix any problems with it.

That's good to hear. Thank you for letting me know.

I notice that your image filenames are very long. The 4th image in your 1st gallery, for example, has 194 characters in it (not counting the file extension).
When working with these files on your computer, you might be reaching the Windows maximum path length (MAX_PATH) of 260 characters. Please see this Microsoft web page for details.
If your image is in your 'Pictures' folder (for example), then this could add approximately 20 characters to the path length (depending on your user account name) but if your images are stored in a deeper file structure, then you could quite easily be pushing the 260 character limit and this might be causing problems.
I would recommend that you reduce the number of characters in your image filenames to see if this helps with your problems.
Incidentally, as noted in the web page I quoted above:

The 4th image has not really disappeared. Your 'Test-5' gallery seems to be an incomplete copy of your 'Test-4' gallery. Your 'Test-5' gallery uses its own set of images (its own 'images' folder) completely independent of the images being used for your 'Test-4' gallery.)

In your 'Test-5' gallery, the 4th image does not appear to be present in your gallery's 'images' folder.
According to your gallery's 'config.xml' file, the 4th image should be located here:

http://www.sirnigelgresley.org.uk/PhotoArchive/Test-5/images/Peter Lane - 4498 on a photo run-through at Appleby on 25th September 1993. Cumbrian Mountain Express with headboard The New Inn Farewell. Photograph taken from far north end of station platform.jpg

... but going directly to that location in a web browser (taking Juicebox-Lite out of the equation) results in an error 404 (file not found).
Please double-check that the image is present in the correct folder on your web server.

The 5th image in your 'Test-5' gallery gives a different error when trying to view it directly in a web browser.

This seems to be due to the use of the '–' character in the image filename. This is not just a regular hyphen '-' but a special character that seems to be encoded as '–' on your web server.

As an image filename forms part of a URL when uploaded to a web server, it would be wise to use only web-safe characters within image filenames. Please see section 2.3 of this document for details.

I would recommend using only the characters noted in the quote above for your image filenames (and not other characters such as spaces, '&' and '–'). (JuiceboxBuilder-Lite can handle all images whose filenames use any or all of these unreserved characters.)

Using shorter, web-safe image filenames might help to solve your problems (both on your computer and on your web server).
I hope this helps.

Edit:
I was typing my reply whilst you posted your last response.
I'm glad that you've been able to figure out the cause of your problem. Thank you for letting me know.
Hopefully my notes above will give a little more information on the nature of the problem.

Please let me know if you're unable to resolve your issue with the blank thumbnail (let me know which gallery you are referring to) and I'll take a look to see if I can help further.

Take a look to see if you have a folder named '.tempGallery' (inside a folder named 'JuiceboxBuilder-Lite') in your 'Documents' folder.

C:\Users\Username\Documents\JuiceboxBuilder-Lite\.tempGallery

If you find such a folder, try deleting it manually (whilst JuiceboxBuilder-Lite is closed).
This should hopefully fix the problem with the 'New Gallery...' and 'Open Gallery' buttons.

Normally, JuiceboxBuilder-Lite will delete the '.tempGallery' folder itself when the program closes but, if the program has crashed, then the '.tempGallery' folder may remain and prevent the 'New Gallery...' and 'Open Gallery' buttons from working.

With regard to the image sizing issue, there is unfortunately a known issue whereby JuiceboxBuilder-Lite will display an error message ("Error resizing image: ‘xyz.jpg’. Possibly the image was too large or invalid. Images must be smaller than 4095 x 4095 pixels.") if the resize dimensions are too large (even if the source images are well within the maximum image bounds).
The problem seems to happen when the Max Width and Max Height are somewhere within the range of between 2364px and 2504px.
The developers are aware of this issue and will hopefully be able to resolve the problem for a future version.
In the meantime, we can only work around this issue by doing one of the following:
(1) Ensure that the resize image bounds are lower than 2364px (or the threshold for your own scenario which is likely to be close to this value).
(2) Resize your images in an imaging program (such as Adobe Photoshop) prior to feeding them to JuiceboxBuilder-Lite and deselect the 'Resize Images' checkbox (on the 'Images' tab) to instruct JuiceboxBuilder-Lite to simply copy the images across to the gallery's 'images' folder (and not process them further).
(3) Create your gallery using a different method. Please see here for a list of plugins available for different programs.

I realise that this may be inconvenient but at least knowing about the problem, we can work around it until it is fixed.

I hope these notes at least help to explain things (even though I am unable to offer a direct solution to the image sizing issue).

No problem!
I'm glad you've got it working. Thank you for letting me know.

I'm very glad to hear that you have been able to resolve your server permissions problem and that all the Showkase Server Compatibility tests now pass OK. Thank you for letting me know.

That would be fine. In order to keep accurate licensing and transaction records, it would be best for you to purchase Showakse-Pro from the purchase page here and for us to then refund you in full for Juicebox-Pro.

There is no need to do this. When you purchase Showkase-Pro, you receive a Juicebox-Pro Single-Site License and the Juicebox-Pro files are exactly the same whether you purchase Juicebox-Pro or Showkase-Pro.

Just let me know when you've purchased Showkase-Pro and I'll get the refund for Juicebox-Pro underway for you.
Thank you.

Thank you for providing the additional information.
As you have uploaded a complete gallery folder ('ephemeralheaven') to your web server, then you can use the baseUrl method of embedding documented here.

In the original code you posted, you have the following line of code:

<script src="pics/ephemeralheaven/jbcore/juicebox.js"></script>

If you had kept this as is and just added the baseUrl entry I suggested, then your gallery would have displayed fine.
However, I notice that you now use:

<script src="jbcore/juicebox.js"></script>

... so the path to the gallery's 'juicebox.js' file is now incorrect.

Use the following embedding code (before your 'juicebox-container' <div>) and all should be well.

<script src="pics/ephemeralheaven/jbcore/juicebox.js"></script> 
<script>
    new juicebox({
        baseUrl: "pics/ephemeralheaven/",
        containerId: "juicebox-container",
        galleryWidth: "100%",
        galleryHeight: "100%",
        backgroundColor: "rgba(255,255,255,1)"
    });
</script>

This should hopefully resolve your problem.
Please let me know how you get on and if you need any further assistance.
Thank you.