hui stop button and pt crashes?

[tomcat]

much too often when i hit stop on my hui, the video turns to black and protools keeps playing audio, but the computer has frozen and i must restart. this happened a few times before 5.0, so i know it's not that. what seemed help last time was updating the rom in the 3940uw scsi board. i have done that, and: defraged drives,
run disk doctor,
rebuilt desktop,
reseated cards,
trashed prefs,
reinstalled os 8.6 update
reinstalled protools,
reconformed movie,
run ramcheck 2.1
asked nicely

what am i missing? this isn't funny anymore.
tonight i will not use the stop button on the hui for the entire session. we'll see...

anyone else seen this?