Matrix Games Forums

I have been playing against the AI and a few PBEM games and haven't had much trouble. But now, I am trying to accept a challenge to play a multiplayer game for the first time. My opponent has guided me through the unfamiliar territory and I have gotten through all the steps except for at the end when it asks me for a password. I tried my forum password, Slitherine password and my Matrix Forum password but nothing seems to work. Help?