Show the error message, after I accidentally clicked "Yes" on "don't show error again"
You could try shutting down all instances of SSMS and deleting the file SqlStudio.bin, which works for clearing out things like the MRU list for server connections. Just note that this will also wipe out other preferences, so you may want to export certain settings (like if you've customized fonts and colors, startup options, etc).

Also, why is SSMS RTM? You should at the very least apply Service Pack 2, if not use a newer version altogether.