damn dude...hhmmm, never heard of this issue with GenB at all. i'm on it also and haven't had any issues like that, i play all my mp3's everyday at work, listen to internet radio, view my pics and have played videos too without a cause for concern or a crash.
did you update to that for PSN access or the PS store?? playing online or anything like that to make you update?? IF NOT, go back down to 5.00 m33-6 and stay there, i would but i play online all the time with my nephew out in KS and i'm in NJ (my only problem with the cfw is no 1.5 kernel support, yet)
IF YOU DO access the PSN/Store, i'd say this too...go back down to 5.00 m33 and reinstall 5.50 genA and then quick update to genB and see if your problem goes away. sometimes these firmwares have to be reinstalled to correct such problems. also what psp are you using?? that could have some thing to do with it also.