Mac build crashes on startup (on some computers)

I have a retina macbook pro and an iMac. A while back I built a mac version out on my macbook and everything worked just fine. About 2 minutes later I built it out again but it crashed the moment I started it. The starting dialog didn't even come up. So I uninstalled unity, deleted All my old builds and a bunch of other things. but it still wouldn't work. So I gave up on it for a while. About 2 hours later I tried it again and it worked. I have know idea how I got it working or if anything I did helped. Now I'm having to same problem with my IMac! But this time it isn't resolving it's self. So if anyone has some insight please share. Thanks a bunch!