My minecraft worked with the snapshot but recently it has been crashing on any world i open but they open on 1.7.2.It's like level.dat has been restarted though because my whole inventory and all block NBT has been deleted. Crash Report attatched.
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Duplicate of MC-45009 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
That wasnt the problem the problem was that all worlds crash for me instead of opening 14w04b
You're using the 1.6 Java which is known to have issues with MC, especially newer versions. Update to the newest Oracle 1.7.0_51 java and see if it still happens.
The MC-45009 is related to why your inventory and other stuff was removed when re-opening your world.
cheers ill try that

That's not how Java works on a Mac.
More information over here: MCL-1049
But, in any case, a small note for you:
Never. Switch. To. Older. Version.
What is the problem then the older version bit was just extra info
The crash is a dupe of MC-38527.