Same problem here. Interesting thing is that we have two machines with Achivements (pretty much the same setup) and in just one of them the error occurs. Had to disable the extension.

 

, DavidGardiner wrote

When this extension is enabled, I get errors building a solution (and these errors go away when the extension is disabled):

1
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(2868,9): error MSB3021: Unable to copy file "obj\Debug\MyProjectAssembly.dll" to "bin\Debug\MyProjectAssembly.dll". The requested operation cannot be performed on a file with a user-mapped section open.