One of Visual Studio’s most cryptic error messages is Server Explorer’s infamous “the given key was not present in the dictionary.” This typically means that you’ve installed a custom data provider, created a Server Explorer connection using that provider, and then uninstalled the provider without deleting the Server Explorer entry.  This pretty much kills Server Explorer: from now on, any time you try to add or remove a connection, it barfs up the useless error.  This means you can’t even remove the dud connection.