I just tried to play multiplayer for the first time and it said "JK2MP.EXE not found", so I look in the directories and sure enough it was missing. I looked at the copy that was on the CD and it wouldn't copy due to a CRC Error.
A friend FTP'ed me the file and it all works, but do I have a bad CD that needs to be replaced???
CRC I belive is a cyclical redundancy check, if you get a CRC error chances are it's a bad copy.