The same problem is discussed here:
http://forum.bsplayer.org/viewtopic.php?p=20956#20956
But ive discovered something. Bsplayer has trouble displaying subs with Xvid encoded OGM files. When i play the same OGM without subs, there's no problem and i can watch it, but when i enable subs, it crashes. I've tried another OGM file, which was encoded in Divx instead of Xvid and that worked great, even with subs on.