It looks like some SG users are affected by an IOQuake bug http://bugzilla.icculus.org/show_bug.cgi?id=4331 (also affects Urban Terror http://forums.urbanterror.info/topic/20 ... ont-start/ )
There seems to have been a viable workaround, wanted to mention it on the forum here because searching for menddef.h returned no results.
Discussion of the problem when running SG 64 bit on Ubuntu 10.04 and 10.10: https://bugs.launchpad.net/getdeb.net/+bug/602625