Hi

So for closing this post, the last status: I could't solve the problems. I had do install the dnn in a new folder and had to copy the sites from the old installation. By this I have seen, that the old installation was after several hours chrashing the hole application pool. And the reason for this was, that the web.config file of the old insstallation was growing in size, because DNN has add houdreds of following entries:

<!--Upgraded by .NET 4.0 Upgrade version 6.1.5 - Date: 5/23/2012 9:23:44 PM-->
<!--<bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0" xmlns="urn:schemas-microsoft-com:asm.v1" />-->

When I copy the original Web.config (38kb) back, and restart the app pool, the old installation run's for several hours, until it crashed again.......

Greetings
Daniel