I have a mac and have the problem where I can get into the login screen, however whenever I log in it creates a grey screen and crashes. So I looked into it and found the problem is with SpoutCraft. Currently SpoutCraft does not support Java 7. So If you want to fix this problem, you have 3 solutions: (1) downgrade to Java 6, (2) Change these files as stated here: http://wiki.spout.org/LWJGL , or (3) wait until SpoutCraft supports Java 7. Personally I have had no luck with options 1 or 2, but maybe it will help you. If you want to see where I got this information, here is the forum link: http://www.spout.org/threads/help-for-mac.6726/#post-89463 .