I have this problem only when i play Multiplayer after some games or 30 minutes always the game crashes with Crysis 3 fails after 24046846983 Bytes or something like that
i know thats memory couse crysis 3 needs 3 gb and dont have enough
but crysis 2 also needs 3 gb and i could play it all time without errors
whats problem now?

Could be some memory leak you are experiencing. I doubt Crytek would release a 32-bit game if the KNEW that it would require more than 3GB of RAM just for that process.

You could try fixing this by enabling the Large Address Aware flag for Crysis 3 by using a third party program. Google it, should be relatively easy to find.