Happened across this glorious error this evening.

Somehow my IServiceProvider COM Object was unregistered from the system through the course of several windows updates, and application uninstalls.

Error:
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)).

Luckily, the guys/gals over on MSDN Social found the fix!

Steps:

1. Open notepad.
2. Copy everything between the "Copy" tags: (From Nick Buse)
   
   
   <COPY>Windows Registry Editor Version 5.00
   
   [HKEY_CLASSES_ROOT\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}]
   @="IServiceProvider"
   
   [HKEY_CLASSES_ROOT\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\NumMethods]
   @="4"
   
   [HKEY_CLASSES_ROOT\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\ProxyStubClsid32]
   @="{B8DA6310-E19B-11D0-933C-00A0C90DCAA9}"
   
   [HKEY_CURRENT_USER\Software\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}]
   @="IServiceProvider"
   
   [HKEY_CURRENT_USER\Software\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\NumMethods]
   @="4"
   
   [HKEY_CURRENT_USER\Software\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\ProxyStubClsid32]
   @="{B8DA6310-E19B-11D0-933C-00A0C90DCAA9}"
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}]
   @="IServiceProvider"
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\NumMethods]
   @="4"
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Interface\{6D5140C1-7436-11CE-8034-00AA006009FA}\ProxyStubClsid32]
   @="{B8DA6310-E19B-11D0-933C-00A0C90DCAA9}"</COPY>
    
3. Paste the text into notepad.
4. Save as a ".reg" file. (Example: IServiceProvider_COM_fix.reg)
5. Right click on the saved file in explorer, and click Merge.
6. Agree to prompt, and you're done!
7. Be very thankful that you didn't uninstall and reinstall SSMS and/or VS like I was about to! PHEW!