aio_error() returning positive values???

[Christopher Smith <x@xxxxxxxx>]

If I understand how aio_error() is supposed to work, it should return 0 in 
the event of a successful AIO operation. Unfortunately, this is what's 
happening to me:
sigtimedwait(...) //waiting for completion signal
int err = aio_error(&aiocb);

err is turing out to be "29". I thought the value would either be 0 or 
negative. What does positive mean?
--Chris