Can't start a server...

Howdy...I'm running Realbot 1.0 with Steam (using the "realfix" thingy, of course). It worked just fine until a few days ago when, as the post title implies, I couldn't start a server. I try to start a listen server and after a minute or so CS closes with an error message saying "SZ_GetSpace: Tried to write to an uninitialized sizebuf_t: ???" followed a few seconds later by an illegal operation error from Half-Life. I suspect that this is related to the latest Steam update, but it there anything I can do to fix the problem?