Hexxit not working when I have Optifine installed.

[Riley10]

My Hexxit works perfectly without Optifine. But when I install it (I've installed it properly) I start a singleplayer world and my game freezes at downloading terrain and then crashed. The odd thing is that I can play on a multiplayer server no problem with optifine installed but I can get onto a singleplayer world. If anyone can help me out that would be great. Note: I have tried over 5 different versions of Optifine and they all have this problem. I have reinstalled Hexxit multiple times also.