this is an utterly bizzare problem, and i can't see why it would be happening, but when i'm running Live5 on my iBook naked (without D/I box etc) Live crashes whenever i remove the plug from the onboard headphone jack socket.
basically, when i unplug my headphones from the iBook, Live crashes. i've never had this problem with Live4 or any other software, i guess it's something to do with the internal re-routing of the sound to the onboard speakers...but it's pretty annoying!