Saw this error today:
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.
Actually, the problem was I had edited the wrong web.config file :-)
In ASP.Net MVC, there's a web.config under the main root, and a web.config under the Views folder.
So, my tip of the day is, make sure you're editing the one you're supposed to be.