While developing a .Net web service I got an error message that made no sense.
"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. "
It turns out that this was caused by me having a backup folder holding a web.config from the deployed version, as well as one or two other 'copy of' versions of the web.config.
Removing these extra files without any changes to my real web.config resolved the issue.
The webpage blogs.msdn.com is where I found the solution to the problem.