Not been able to work on this for a while, but I've got a chance to pick it up again now.

 

The Zip file in the link doesn't exist.

 

Also, I have followed your last instructions to the letter, giving the NETWORK SERVICE account write access to the directory, and the error still occurs.

 

If you look at the stack trace in the error message I posted, you can see that CE calls the Path.GetTempPath() method, which requires unrestricted CAS Environment permission (see: http://msdn.microsoft.com/en-us/library/system.io.path.gettemppath(VS.71).aspx). In a medium trust environment, this is not available.

 

To demonstrate, put the following line in the system.web section of yourweb.config, and attempt to access any of the toolbar items that open a file dialog:

 

You should get an error message similar to the one I posted.