For no reason a rebuild of a .NET MVC project created these errors that wouldn't go away with restarts, cleans, running as administrator, etc:
Error 383 Unable to copy file "..\root\foo\bar\thing\test.thing.xml" to "bar\thing\test.thing.xml". Access to the path 'bar\thing\test.thing.xml' is denied
As detailed here: https://stackoverflow.com/questions/2895898/visual-studio-build-fails-unable-to-copy-exe-file-from-obj-debug-to-bin-debug
The only thing that worked for me was the answer by https://stackoverflow.com/users/2435679/adrian-booth
When I have come across this problem it is to do with the Fact that the project I am trying to build is set as the Startup project in the solution making the .exe in the obj folder locked ( it also appears in your task manager,) right click another project in your solution and choose set startup project. This will release the lock, remove it from task manager and should let you build.
Took me about an hour to find this!