As I mentioned earlier, Juicebox v1.4.2 is certainly able to use a PHP file to dynamically generate XML data for a gallery.
In fact, WP-Juicebox (the Juicebox plugin for WordPress) does this and works fine with Juicebox v1.4.2.

In order to investigate further, I would really need to see your gallery live on your web server so please post the URL to your gallery or let me know if you would rather that I contact you via email so that you can email me the URL to your gallery instead.

I meant for you to try loading Google into an iframe (in a similar manner to how you are currently loading your Juicebox gallery) rather than just display 'http://www.google.com/' on your web page as plain text to see if the problem occurs with any content in an iframe and not just with a Juicebox gallery (to determine whether or not the problem is directly related to Juicebox or the iframe).
Try replacing:

http://www.google.com/

... with:

<iframe src="http://www.google.com/" style="border:0px #FFFFFF none;" name="SimpleViewer" scrolling="auto" frameborder="0" marginheight="0px" marginwidth="0px" height="100%" width="100%"></iframe>

... to see what happens.

No matter what happens with the test above, a possible solution should be to just embed your gallery directly into your web page (using the baseUrl method of embedding) rather than using an iframe.
Try replacing:

<iframe src="index_htm_files/JUC01test/index.html" style="border:0px #FFFFFF none;" name="SimpleViewer" scrolling="auto" frameborder="0" marginheight="0px" marginwidth="0px" height="100%" width="100%"></iframe>

... with:

<!--START JUICEBOX EMBED-->
<script src="index_htm_files/JUC01test/jbcore/juicebox.js"></script>
<script>
  new juicebox({
    baseUrl : 'index_htm_files/JUC01test/',
    containerId : 'juicebox-container',
    galleryWidth : '540',
    galleryHeight : '291',
    backgroundColor: '#222222'
  });
  </script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

If this still does not work, then you may need to delay the loading of your Juicebox gallery until the container into which your gallery is embedded is visible on your web page. You could put the embedding code into a JavaScript function and run it when your icon is clicked, using code such as the following:

<!--START JUICEBOX EMBED-->
<script src="index_htm_files/JUC01test/jbcore/juicebox.js"></script>
<script>
    function loadGallery() {
        new juicebox({
            baseUrl: 'index_htm_files/JUC01test/',
            containerId: 'juicebox-container',
            galleryWidth: '540',
            galleryHeight: '291',
            backgroundColor: '#222222'
        });
    }
</script>
<div id="juicebox-container"></div>
<a href="#" onclick="javascript: loadGallery(); return false;">Click here to load gallery.</a>
<!--END JUICEBOX EMBED-->

That's great!

Images #9, #13 and #23 have a different aspect ratio to the other images in your gallery. They are very long and thin. Image #9, for example, has dimensions of 275 x 768. If you compare the thumbnail for image #9 with its corresponding main image, you will notice that the entire width of the main image is displayed within the width of the thumbnail. However, to create a thumbnail with the dimensions you use, the only way to do so (to get a square from a rectangle) is for JuiceboxBuilder-Pro to crop the top and bottom of the image.
JuiceboxBuilder-Pro does not allow you to position the focus of the crop (it is always the centre of the image) but you could create your own thumbnail images if you like (in an imaging program such as Adobe Photoshop) and replace any existing ones in your gallery's 'thumbs' folder.

Please see this FAQ which seems to be relevant to your problem:
My images show locally, but not when I upload them to my website. Why?

Also, try opening one of your gallery's images from your web server directly in your browser to see if it displays OK (taking Juicebox out of the equation). If it does not display OK, then check the permissions of the 'images' and 'thumbs' folders and the image and thumbnail files themselves on your web server to make sure that they are not too restrictive and can be read by the browser. Default permissions of 755 for folders and 644 for files should be fine.

If you continue to experience difficulties, please post the URL to your gallery's web page so that I can take a look and help further. (http://ligthtstuff/bsci is an incomplete web address.)

This is the code that you would use if you wanted to embed the gallery into an existing web page alongside other content, following the instructions here (see Step #3).
If you just want to display the gallery on its own web page, then you can use the gallery's 'index.html' file (generated by JuiceboxBuilder) and you do not need to use the embedding code from the 'Publish' tab.

I really cannot think of anything else which you could try.
It seems very strange that JuiceboxBuilder-Pro cannot open a gallery on your Mac which I can open fine on my own PC.
If I think of anything else which might help, I will be sure to post back.

If you plan to rebuild your gallery, you should hopefully at least be able to load your existing gallery's XML file as a preset ('Presets -> Load Preset...' from the drop-down menu at the top) to save you from having to set all the configuration options individually.
Just add the images to your new gallery and then go to 'Presets -> Load Preset...' and navigate towards your existing gallery's 'config.xml' file. All the configuration options from your existing gallery should be applied to your new gallery in a single action.

With Juicebox-Pro, you would be able to create the gallery from your image but not the rest of the page. Juicebox-Pro is an image viewer/web gallery and not a complete web design package. You would need to somehow create the web page (either manually or using web design software) and then embed your Juicebox gallery in it following the instructions here.

Showkase, on the other hand, is able to create a complete portfolio website.
Showkase has full support for Juicebox-Pro (and SimpleViewer-Pro) and the galleries can be created within the application itself in a web browser interface (or created with JuiceboxBuilder-Pro and imported).

Showkase can also create non-gallery pages (About, Basic and Contact pages) where you can add information about yourself (or any other content you like).

It may not be possible to exactly replicate the web page from your image using Showkase but you would certainly be able to include most of the features (using a logo in your site's header, having a menu for users to navigate throughout your site, contact details, etc).

All of this is done automatically within the Showkase interface without the need for any manual coding at all.

Please take a look at our demo Showkase sites to see what can be achieved with Showkase.

Showkase can be purchased as Showkase-Standard (which comes with Juicebox-Lite and SimpleViewer-Standard, the free versions) or Showkase-Pro (which comes with Juicebox-Pro and SimpleViewer-Pro).
(The only difference between Showkase-Standard and Showkase-Pro is the bundled viewers.)

I hope this information helps.

There are a couple of things that might be causing your problem.

(1) Your web page does not have a Doctype Declaration. It is important that each HTML document uses a Docytype declaration in order to inform the user's browser what set of standards the code on your web page should conform to. Add an appropriate Doctype declaration to your page.
From the look of your code, you could use the HTML 5 Doctype. Add the following code to the very top of your HTML page (before the opening <html> tag).

<!DOCTYPE html>

(2) As your gallery's height is expressed as a percentage, please see this note for Using Percentage Heights. Essentially, make sure that all parent containers of your gallery have heights explicitly expressed via CSS.
Alternatively, try taking your gallery out of the table on your web page (as the gallery is the only element in the table) and position your gallery on your web page using CSS instead.

Unfortunately, there is currently a known bug (which should hopefully be fixed in the next version of Juicebox) whereby the value of the expandInNewPage configuration option can change the scale of the embedding page. This may be the cause of your problem.
If your gallery currently sets expandInNewPage="TRUE", then try setting expandInNewPage="FALSE" (in JuiceboxBuilder-Pro's 'Customize -> General' section). Conversely, if your gallery currently sets expandInNewPage="FALSE", then try setting expandInNewPage="TRUE".
(Alternatively, try setting expandInNewPage="AUTO" if "TRUE" or "FALSE" do not work.)

Hopefully this will help, although if v1.4.0 works fine for you just now, you may wish to continue using it until the next version (with the fix for this problem) is released.

If this does not help, then, in order to investigate further, I would really need to see the problem for myself so please post back with the URL to your gallery so that I can take a look for myself. Thank you.

This may cause problems as, even though the plugin folders are named differently, you will essentially have two plugins with the same name. Try temporarily moving one version of your WP-Juicebox plugin outside your 'wp-content/plugins' directory.

This sounds like the 'wp-juicebox/wp-juicebox.php' file may have been modified or has somehow become corrupt or incomplete.
Try reinstalling WP-Juicebox from scratch.
(1) Download WP-Juicebox from the link on this web page.
(2) Delete all WP-Juicebox folders from your 'plugins' directory. (Make a backup copy of them first before deleting them.)
(3) Install WP-Juicebox following the instructions on the page linked to in (1) above.

If, after reinstalling the plugin, you still see this error message, please post the URL to the web page which displays this message so that I can see the problem for myself and help further.
WP-Juicebox handles all paths automatically and, under normal circumstances, this message should not be displayed.
One possible reason for this message being displayed in a WP-Juicebox gallery would be if the 'wp-juicebox/config.php' file was missing (or had permissions which were too restrictive). If this were the case, then reinstalling the plugin should solve this problem, too.

Thank you for trying. It was worth a shot. As unlikely as it sounds, it worked for a different user who was experiencing a similar problem to your own (which is why I suggested it).

Thank you for providing your zipped gallery.
I can open it in JuiceboxBuilder-Pro v1.4.2 without any problem so there certainly does not seem to be a problem with the gallery files themselves.

Please check the permissions on the gallery files on your Mac to see if this might be the cause of your problem.
Also, make sure that you are not trying to open the gallery folder from a restricted file system or network drive. Try copying your gallery folder to a different location on your hard drive (such as your desktop) before trying to open it to see if this helps.

Is your problem that the 'Open Gallery...' button is completely ineffective (nothing happens when you click it) or that you are able to select the gallery folder but the gallery does not open when clicking 'Select Folder'?
If it is the second of these two scenarios, then try replacing the 'jbcore' folder in your gallery folder with a fresh copy of the 'jbcore' folder from the Juicebox-Pro downlaod zip package ('juicebox_pro_1.4.2/web/jbcore/') before trying to open the gallery.
If this still does not work, then, if possible, please zip the gallery, upload it somewhere and provide a download link so that I can try to open the gallery and replicate the problem for myself.