I'm pretty sure this is a Cross-Origin issue. I've been able to replicate the problem myself in a test scenario but, unfortunately, I've been unable to find a good solution.
Normally, your gallery is hosted on gallery.charleychau.com but is displayed on charleychau.com.
However, when the gallery is expanded from the Splash Page, it is displayed via the 'full.html' page within the 'jbcore' folder on gallery.charleychau.com (swapping the domain on which the gallery is being displayed). To complicate matters, Juicebox passes configuration options to the 'full.html' page via a session cookie.
I've tried adding the following line to the .htaccess in my test scenario file to add cookie support to the CORS solution.
Header set Access-Control-Allow-Credentials true
... and I've tried adding the full .htaccess file:
Header set Access-Control-Allow-Origin "*"
Header set Access-Control-Allow-Credentials true
... to both domains (in theory to allow access in both directions) but it does not work.
The only thing I've been able to think of would be to set expandInNewPage="FALSE" to prevent the gallery from being displayed via the 'full.html' page when it is expanded from the Splash Page. The gallery will then be expanded on top of the embedding page (still on the charleychau.com domain) which may cause a scaling problem on iOS devices. (Expanding the gallery on a page of its own is designed to avoid this potential scaling issue.) It's certainly worth a try, though.
Alternatively, you could keep expandInNewPage="AUTO" and lock the viewport of your gallery's web page.
Please see the Expand Gallery Behavior support section for details.
I hope this is a suitable workaround for your problem (as it seems to work well in my test scenario).