Me again,

after a "litte" break i went back to analyse  the problem...

We still have the problem in Dnn 3.1. But I've some more details.

The error only occurs for new files that are not synchronized. When I sync the Filesystem and Database with the function (provided in Portal Filemanager) all will work fine. Adding a new file with the "insert image" dialog and use the new image... the system will log me out while saving the page.

Another issue... I can't catch the problem in the debugger. Stepping through the updateprozess in debugger won't cause the problem.