It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level.  This error can be caused by a virtual directory not being configured as an application in IIS

I got this error when i tried to compile my web application using Visual Studio 2005. This was because there were more than one web.config files inside the application folder (inside subfolders). When i removed that, this issue got solved.

Thought that this may help you sometimes [;)]