Help me understanding a stacktrace?

Generally SIGABRT (the signal that the operating system terminated your program with) means that there was a call to the abort() or terminate() function. This is the function used if there is an unhandled exception, so that's probably what your problem is. Also evidencing the case of an unhandled exception is the fact that the stack trace shows Thread 1 calling "objc_exception_throw.

You need to symbolicate this crash log, which will convert 0x000029cc 0x1000 + 6604 from gibberish into lines of code, and allow you to see what part of your code is throwing an exception. In theory you can do this by dragging the crash log into XCode 4's Organizer window, but there are reports of a bug in XCode 4 that affects symbolication, so you may have to use one of these workarounds.

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