finding release errors


I have a bit of a problem with some code - when I get to [pool release]; it exits with either a signal 10 or signal 11. I suspect I'm releasing something too often or not enough, but have no idea where to start looking. Any suggestions?

(and where can I find the meanings of "signal 10 (SIGBUS)" & 11?)
I get those too when I release some things. My guess is the objects are on autorelease, so releasing them manually causes access errors (BAD_ACC_EXC or something like that).

I try to stick to the so-called convenience constructors that are always autoreleased--things like [NSString stringWithXXX]