Could be a bad MUI setup or a buggy class...but apart from that I've never heard of this problem before. You could try updating all your classes, but short of that I don't have a clue. Even before I registered AmIRC didn't crash like that. Then again, the original 3.5 is very buggy...
And if you want to experiment I'd recommend you do it from RAM or an SFS/PFS partition in future - much safer.
