Try re-uploading your 'jbcore' folder to your web server to ensure that all the files are present and correct in case any resource files are missing or were somehow corrupted during the initial upload.
Didn't work. No noticeable change.
Try using absolute URLs in your embedding code rather than relative URLs (for the path to the 'juicebox.js' file, the baseUrl and the configUrl). If this helps, then perhaps there is a rewrite rule in an .htaccess file on your web server which is causing the problem.
Oddly, this caused the dreaded "config.xml not found" error. Removed baseUrl and still got it.
Try setting expandInNewPage="FALSE" (in JuiceboxBuilder-Pro's 'Customize -> General' section) and locking the viewport of your embedding page. Please see here for details.
I tried this previously, but it causes the page to view zoomed in with no way to pinch.