Yeah, next_ghost, that wasn't very helpful. I've never seen this error message before. It's not the standard "wrong qvm/tremded combo" error which is mentioned in my guide. It could be a different error message with the same cause, but as I say, I've never seen it before.
Having said that, Mexel, I don't know what else it could be. So I'll elaborate on next_ghost's theme and say that you should be ABSOLUTELY SURE that you have tjw's tremded.exe AND tjw's game.qvm, that you put them in the right places, and that there are NO OTHER tremded.exe or game.qvm files anywhere else.
To rule this out it would probably help for you to post the complete contents of:
C:\Program Files\Tremulous
C:\Documents and Settings\YourUserName\Local Settings\Application Data\Tremulous
and their subdirectories.