The access to the path bin\ is forbidden exception while building - Visual Studio 2008 and TFS

I had this strange error yesterday and it took me some time to understand what is going on.
It appeared that the bin folder of the main project is under source control, so TFS was locking the folder, the subfolders and the files.
In order to resolve it - checkout the bin folder in Visual Studio and then build.
The build should be OK.
Then you can Undo Changes on the folder and everything should work as it was before.

Hope this helps someone ...