If you open up a Windows Explorer window and browse to %appdata%\MayhemIntergalactic (which is equivalent to e.g. C:\Documents and Settings\YourUserName\Application Data\MayhemIntergalactic on Windows XP - note that Application Data is a hidden folder), do  you see any log files? If you cause the crash you're describing and then open up the latest log file and look in it, is there anything interesting in there?

Here's exactly what the log includes:

Renderer startup took 418515 microseconds
Audio startup took 2244198 microseconds

And that's that. 

Otherwise, I'm out of ideas without consulting a debug log. If you send me an email, I'll get you a debugging version ASAP.

I will do that. Thanks for all your help, Chris.  I greatly appreciate it! 

The only firewall I have installed is the built-in one that comes with XP.  I disabled it and tried again...same thing is happening.

[not]

Yeah, I have an active and full internet connection and Steam is not in offline mode.  And it is indeed a guest pass, not the demo.

Hi!

I've currently got a guest pass for Mayhem on Steam.  The single player is neat and all, but whenever I click on Internet or Local under Multiplayer, I get a Critical Error box with the words Access Violation; needless to say, the game closes after that. 

Any ideas?