Microsoft Visual Studio
Unexpected error encountered. It is recommended that you restart the application as soon as possible.
Error: Unspecified error
Line number: 5892
One reason you get this is because you have a file on your local disk, but not in VSS. This only happened with SLN files for me, but may happen with other files as well.
You need to open up the VSS provider, SourceOffSite (SOS), or whatever you are using and manually add the file. Then go back to VS and Change Source Control again.