Hi,

the solution is: This behaviour is caused by wrong  trust Level for DNN in your web.config File.

Options for the trust level (more details avaible at MSDN or under http://msdn2.microsoft.com/en-US/library/tkscy493(VS.80).aspx) are:

<trust
   level="[Full|High|Medium|Low|Minimal]"
   originUrl="URL"
   processRequestInApplicationTrust = "[True|False]"
/>

Please have a look at the possible  parameters/options.

So you have to decide with trust Level you can/want use (e.g. restriction by your Provider). Examples are:

A.) If you want to run DNN under Medium Trust, edit your web.config file like: <trust level="Medium" originUrl="" />

B.) If you want to run DNN under Full Trust, edit your web.config file like: <trust level="Full" originUrl="" />

In my case the trust level was set by installtion of Windows Sharepoint Services. The way described solves the behaviour.

Best Regards
Marcus