Hi,
   I seem to be getting this error but cannot figure out why. I have removed Master Pages and all user controls because other sites seem to suggest this causes this error. I have also removed using the login pages. Yet I'm still getting it. Does anyone have any information on preventing this error from occuring? Is there a fix for this? MS wants me to pay 245.00 hourly for a fix to this.

I was able to find this on google and it fixed the problem. Other sites suggested several web.config changes etc. This suggestion worked for me so I wanted to pass it on especially since this error can drive one crazy!!!

Here's the link I found this solution at:
http://forums.asp.net/1144604/ShowPost.aspx. See the response at 1:44 by ScottGu...

The problem you are having above is that the "/foldername" directory is not marked as an application, yet the \bin directory containing your assemblies is probably contained underneath it. As such, ASP.NET isn't looking for your assembly in the right place -- instead it is looking for it in the \bin directory underneath the root site/application on your system (note how the error message above starts with the text "Server Error in '/' Application").

To fix this, you should go into the IIS admin tool, right click on the /foldername directory and pull up its properties. You'll then want to make it as an application within IIS (by clicking the "create" button). The assemblies in the \bin directory should then resolve correctly.