A lot of CS players seem to get this, also so:
Many people have been getting a mysterious "Expected { got (B3)" error when trying to play Half-Life or Team Fortress Classic multiplayer. This is a (temporary) problem with Sierra/Won.net's network system and should be fixed within a few days. Meanwhile, there's a simple work-around that will get you back into the fray right away -- just delete the Half-Life temp file "favsvrs.dat".