I click the "play" button.
Every thing starts up, except the minecraft window.
A few seconds later a window pops up saying minecraft failed to open, and this was left in the log box:
Client> 2013-06-25 13:53:54 [CLIENT] [INFO] (Session ID is ${auth_session})
Client> Invalid memory access of location 0x0 rip=0x0
Client>
Game ended with bad state (exit code 139)
Deleting /Users/admin/Library/Application Support/minecraft/versions/1.6/1.6-natives-1372186433079680000