It also sometimes happens, if you have a map that isn't team arena compliant
such as PieDM1 (i Love that map)
and CTF_Marioopposingcastles (Also very Cool)
but i'd check what tab said first
as i have tried running generations on point release 1.30 and it's been fun watching half of the shaders and textures being missing
other than that try taking out all your other maps, the ones usually in baseq3 folder and putting them back in one by one as it could be that
also check your settings in the display, i have had problems with that as well
especially if you have a Nvidia card