I received this error when trying to open Visual SourceSafe 2005 from Visual Studio 2010
Installing the following patch fixed the problem:
http://archive.msdn.microsoft.com/KB976375/Release/ProjectReleases.aspx?ReleaseId=3479
Installing the following patch fixed the problem:
http://archive.msdn.microsoft.com/KB976375/Release/ProjectReleases.aspx?ReleaseId=3479