I recently started getting this error intermittently when running or building a solution in Visual Studio 2010:
The specified task executable cmd.exe could not be run. The process cannot access the file 'c:\temp\etc' because it is being used by another process.
There are similar problems reported elsewhere, due to things like two projects building to the same folder, or anti-virus issues, but none of them are the problem in this case. I've reduced the solution to a single project and it still happens.