Visual Studio 2010 source control integration doesn't work with files outside the solution folder
===

I have some header and cpp files that are shared between 2 projects, so I have put them in a folder named Common:

    C:\Workspace\Common\utils.h
    C:\Workspace\Common\utils.cpp
    C:\Worspace\Project1\Project1.sln
    C:\Worspace\Project2\Project2.sln

The 2 files utils.h and utils.cpp are added to both projects, and they're added to SourceSafe as well. However, "File->Source Control->Check Out" from the menu is disabled for those 2 files, even though they're added to the project.

Is this because they're outside the solution's folder?