As 'whoever it was' has messed up pretty badly, you're currently unable to join any servers. You can use this fix to continue playing in the mean time; vgui_allowhtml 0 Enter into console prior to joining a server. Expect a significant reduction in players until they can be bothered to fix it however.
Thanks for doing the research on finding how too fix gmod for now. Just wish our fellow players knew how to do this. But hope we get popular tonight. I will come on now.