I attempted to play quakeworld by downloading the client from ftp://ftp.idsoftware.com/idstuff/quakeworld/

However it does not recognize pak0.pak as a registered version of quakeworld. I have verified that my pak0.pak is registered as its checksum matches the one for Registered Version 1.06 according to http://quakewiki.org/wiki/pak0.pak

Does anyone know what is wrong? I really would like to play quakeworld.