Hello Thomas,
I'm not using languages in the extension, I don't think it comes from this.
I've searched a bit, it seems there are other people that have similar problem with other extensions too.
From this thread, last post:
http://forum.joomla.org/viewtopic.php?f=470&t=252418&st=0&sk=t&sd=a&start=30
- chmod all files and folders to 777
- Another way, apparently, was to change FTP-settings in Global Configuration to NO.
- Another way, go to the server settings in Global Configuration and change Path To Temp-Folder from
/temp
to the more correct
tmp
Hope one of these solutions will help you