Problem with design->customize

Hi I’m currently running FullFrame Pro on my 2 networked sites. I have a problem with the Appearance/Customize option. I have 2 (nearly) identical sites, one in English, the other in German. Same structure, pages, posts, plugins, etc., only the content is translated. No problems when I click "appearance->customize" in the English site, the page for customization is displayed correctly. This site is located here: http://new.aquariumcomputer.com/en/ (not yet translated completely) But when I try to do the same on my German site only a blank screen is shown. This is the site: http://new.aquariumcomputer.com/de/ I am not sure, but this seems to be an issue since the update from 3.2->3.3, didn't recognize it before. Already tried 3.4 but didn't change anything. This is the URL to the cutomization page of the English site which works: http://new.aquariumcomputer.com/en/wp-admin/customize.php?return=%2Fen%2Fwp-admin%2F This is the URL of the German site which doesn't work: http://new.aquariumcomputer.com/de/wp-admin/customize.php?return=%2Fde%2Fwp-admin%2F Any help would be very much appreciated since we can't finish our project due to this issue and the deadline is approaching ... thanks.