Unity 4.2 crash when editor recompiles project

Hi there, I have a project that builds fine in Mono, but as soon as I switch back to Unity 4.2 the editor recompile kicks in. The loading spinner does its thing and stops (which usually indicates a reload in progress and should last a couple of seconds). Then Unity hangs every time. I've tried cleaning my build, deleting all temp directories etc and reinstalling Unity. I'm on a 2009 15" Macbook Pro. Any ideas? Are there any other settings files hidden around I should get rid of to start from a "clean" install? Thanks, Jonny