Recently I got following error when trying to add a Web Reference to VS2008:
The web services enumeration components are not available. You need to reinstall Visual Studio to add web references to your application.

I have no idea why this error suddenly appeared.
However, I did find a solution to this issue.

I executed ‘devenv /ResetSkipPkgs’ from the command line in a VS2008 command prompt.
This did the trick for me.