Whenever I join my server and look at any slime block placed before snapshot 14w18a, my client crashes. I can't recreate this in a singleplayer world and I've tried redownloading and reinstalling the server jar multiple times but nothing seems to help. I've attached the crash report below.
This is not because of Slime Blocks, the game crashes when it renders Item Frames as your crash report shows. Therefore Duplicate of MC-54008.