I have encountered an error that was driving me nuts:
Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.VisualStudio.OLE.Interop.IServiceProvider'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{6D5140C1-7436-11CE-8034-00AA006009FA}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)). (Microsoft.VisualStudio.OLE.Interop)
Googling and Binging revealed I'm not the only one to have this issue. I even tried the fixes here:
http://social.msdn.microsoft.com/Forums/en-US/sqltools/thread/6d0f23e5-14fd-4a32-b37d-33458c339b14
with no luck. This is the second machine (same machine actually, just reinstalled Windows 7 RTM) and had the same error occur. I got lucky this time, though, in that I noticed it started happening immediately after I installed Source Gear Vault version 3.1.5. Figuring that Vault was the most recent installed item, I tried uninstalling it and voila, the problem was gone.
I know that's not a solution for most people - I'm lucky in that I only need Vault for a little bit as we're moving to another source control provider. I also suspect it's not an issue for most folks as 3.1.5 is a really old version of Vault. But at least I finally know what was causing the error.