Site in BIG trouble - English version (and French) not working properly any more

Hey there,

just tried with @Michael Bisset to solve the problem in the chat - however, that did not work out, the problem seems to be bigger.

watch this page, please:
(here only a minor issue: contrary to what was once (without changing anything except for plugin updates) the thumbnails do not show rounded corners any more

But then try to switch to English (or French) - then it gets really messy. Debug mode shows the following:

Fatal error: Cannot use object of type WP_Error as array in /var/www/web10/htdocs/wp-content/plugins/intense/inc/photosource/Intense-photo.php on line 115

Tried to deactivate all plugins except for Intense and WPML (the first one providing the used shortcode that works only on my German page now - but used to work on the other pages, too) - the second needed to be able to switch languages... the problem still was there...

Also tried to "downgrade" intense from 2.5.3. to 2.0.1 - no success (except for the page "hotel" which then worked in both English and German)

Support access is granted...