It sounds like you are doing everything as you should.
The current version of the Juicebox plugin for Photoshop (v1.5.0) hosted on the Adobe Add-ons website has been tested with Photoshop CC 2015.5 and auto-installs successfully via the Creative Cloud Desktop App on my own system.

You should get a confirmation message in the Creative Cloud Desktop App's 'Home -> Activity Stream' to let you know that the plugin installed successfully.
The only problem I encountered whilst testing the auto-install was when I installed a new version of Photoshop alongside an older version. I found I had to reboot before attempting the plugin installation again.
Make sure that your Creative Cloud Desktop App is up to date (v3.8.0.310). If you are not already using the latest version, updating it might make a difference.

If you are having trouble with the auto-install mechanism, I would recommend installing the plugin manually.
Just download the 'Photoshop CS2 to CS6' zip version from the plugin's support page and follow the manual installation instructions. The resulting files in the 'Presets/Scripts/' folder will be exactly the same as if installing the .zxp version. Only the packaging of the files differs between the two.

It looks like you'll need to break out of PHP to enter the gallery's HTML embedding code and open up a new PHP section after the embedding code:
Try replacing:

echo ' **code goes here to work with logged-in users of SMF**  ';

... with:

?>
<script src="https://www.mydomain.tld/storage/support/jbcore/juicebox.js"></script>
<script>
    new juicebox({
        baseUrl: 'https://www.mydomain.tld/storage/pictures/galleries/',
        containerId: 'juicebox-container',
        galleryWidth: '100%',
        galleryHeight: '500px',
        backgroundColor: '#222222'
    });
</script>
<div id="juicebox-container">
    <noscript>
        <p>You need Javascript to view the gallery on this page.</p>
    </noscript>
</div>
<?php

Hopefully this will work for you.

You're welcome!

You're welcome!

If you use Showkase for your website and Juicebox galleries, then there will be no need to worry about any embedding code or file structure. Showkase will handle it all for you.

Don't forget that 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.

If you do purchase Showkase, be sure to check out the Getting Started guide here.

@bherman

Thank you very much for your suggestions.

I realise that you have seen this yourself but for other users reading your suggestions, there is a single-page solution which might be useful in this forum post.

Please double-check that the gallery folder you are selecting has a 'config.xml' file inside it.
(JuiceboxBuilder will not open a gallery where the XML file has been renamed or moved.)

Also, make sure that the gallery folder you are trying to open is not in a restricted file system or on a network drive.
Try moving the gallery folder to your Desktop (or a differently location to where it currently is) and try opening it from there.

Also, it might be worth checking to see if you have any security software installed which might somehow be interfering with JuiceboxBuilder's functionality. If you do have any security software installed, make an exclusion rule for JuiceboxBuilder to see if this helps.

I'm glad you've been able to resolve your problem.
Thank you for posting back to let me know.

For other users reading this thread, here are a few notes for clarification.

Upgrades are free within the same major version number.
You can use the link from your purchase email to download the latest version of Juicebox-Pro.
The download link always points towards the latest version rather than the version you purchased.
Please see the Upgrading Juicebox support page for more details.

Juicebox-Lite is free (Juicebox-Pro is not).
Juicebox-Lite comes with JuiceboxBuilder-Lite (the desktop application) and the Lite version of the Lightroom plugin.
Juicebox-Pro comes with JuiceboxBuilder-Pro and the Pro version of the Lightroom plugin.
Lite versions of JuiceboxBuilder and the Lightroom plugin feature only Lite configuration options whereas Pro versions feature all configuration options.

Juicebox-Lite can be downloaded from (and Juicebox-Pro can be purchased from) this page.

Instructions for installing JuiceboxBuilder can be found in the User Guide. You can upgrade JuiceboxBuilder by just running the new 'JuiceboxBuilder.air' file. However, if you are upgrading from a very old version of JuiceboxBuilder, you might find that you need to uninstall the old version first before installing the new version.

No problem. I've split your post into a new thread.
The 'Post new topic' link is just above the second blue bar at the right-hand side of the page (once you've selected the 'Juicebox-Pro Support' or 'Juicebox-Lite Support' forum).

(1) On Showkase's 'Pages' tab, click 'New Page', create a Gallery Index Page and click 'Save'.
(2) Now, still on the 'Pages' tab, just drag and drop your Juicebox Gallery Pages (drag and drop the page names in the tree on the left hand side) onto the Gallery Index Page (in the order you want their thumbnails to be displayed).
(3) Click 'Save' and 'Publish'.

Each Juicebox Gallery Page listed under the Gallery Index Page will be represented by a thumbnail image.
By default, the thumbnail image will be the first image in the gallery. If you like, you can change this to be any other image from the gallery by editing the Juicebox Gallery Page, going to the 'Images' tab and selecting a new image in the 'Index' column. Be sure to republish your site after making this change.

Incidentally, I notice that you have a large logo that is taking up a little more that the regular header height and is pushing your Juicebox galleries down their respective pages.
You can compensate for this by going to 'Site -> Customize Theme -> Gallery Pages' and entering a negative pixel value (e.g. "-100") in the 'External fit px' input field.
This will reduce the height of each gallery by the amount you enter and all your galleries will be able to be seen in full (without the need for vertical scrolling) regardless of the height of the user's browser window.

I hope this helps.

Are you referring to a folder that you are trying to save the gallery to (or a folder that a source image is in)?
What error are you getting?

You should be able to use the ø character in a gallery (although it might not be wise to do so).

As a test, I've just successfully created a gallery with JuiceboxBuilder-Pro v1.5.0 (on a Windows 10 PC) using an image with a ø character in its filename (from a folder with a ø character in its name) and saving the gallery to a new folder with a ø character in its name. The gallery is saved correctly, uploads to my web server correctly (via Filezilla), displays correctly and the the ø character also appears in the image caption correctly.

However, as image filenames and gallery folder names form parts of URLs when uploaded to a web server, it would be safer to use only web-safe characters. Please see section 2.3 of this document for details: https://tools.ietf.org/html/rfc3986#section-2.3

You should have no problems (with JuiceboxBuilder-Pro, your web server, FTP software or browsers) when using any or all of these unreserved characters.

I'd stick with web-safe characters for file and folder names and keep accented and special characters for image titles and captions.

I notice that your gallery has a height of 88%. I think it would be difficult to get a clean working solution (with either CSS or JavaScript) using such a gallery height. The suggestions below use a gallery height of 100% so that the gallery fills its container and when JavaScript is used to determine the height of the container, you know that the gallery is the same height.

Take a look at the Using a Resizable Gallery with a Header support section.
The View Resizable Gallery with Top Menu Example has a header and a footer (both with fixed heights) and the gallery takes up the remainder of the available space (no matter what size the browser window is) without any scrollbars.
You can view the source of the web page in your browser and copy/modify the code to suit your own needs (removing the footer, changing the header content and swapping the sample gallery with your own).
The example also switches between galleries (something you might not need) and uses an external CSS file.
Here is a single file solution that you might like to use. (The code should be fairly easy to follow.)
To see it in action, create a sample gallery with JuiceboxBuilder-Pro (just use all default settings) and use the following code as the gallery's 'index.html' file.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8" />
        <style type="text/css">
            html, body {
                height: 100%;
                overflow: hidden;
            }
            body {
                background-color: #222222;
                margin: 0px;
            }
            #header {
                background-color: #222222;
                color: #666666;
                font-family: sans-serif;
                font-size: 20px;
                height: 50px;
                padding: 10px 0px;
                text-align: center;
                width: 100%;
            }
            #wrap {
                width: 100%;
            }
        </style>
        <script type="text/javascript" src="jbcore/juicebox.js"></script>
        <script type="text/javascript">
            var jb;
            function doLayout() {
                var windowHeight = parseInt(window.innerHeight ? window.innerHeight : $(window).height());
                var headerHeight = parseInt($('#header').outerHeight(true));
                var galleryHeight = windowHeight - headerHeight;
                $('#wrap').height(galleryHeight);
                if (jb) {
                    var galleryWidth = parseInt($('#wrap').innerWidth());
                    jb.setGallerySize(galleryWidth, galleryHeight);
                }
            }
            $(document).ready(function() {
                doLayout();
                $(window).resize(doLayout);
                jb = new juicebox({
                    containerId: "juicebox-container"
                });
            });
        </script>
        <title>Test</title>
    </head>
    <body>
        <div id="header">
            <span>Header</span>
        </div>
        <div id="wrap">
            <div id="juicebox-container"></div>
        </div>
    </body>
</html>

You're welcome!
I'm glad you've got it working.
Thank you for letting me know.