After installing Microsoft Visual Studio 2010 sp1 I was getting the error:

Fixing the VS2010 sp1 error: The command you are attempting cannot be completed because the file …vdproj is under source code control and is not checked out

When I build a solution.

Solution

Downloading and installing the hotfix:

http://connect.microsoft.com/VisualStudio/Downloads/DownloadDetails.aspx?DownloadID=35848 solved my problem