large world crashing

My world is 400MB + Large and every time i load it up it crashes almost straight away. this has only happened in the most recent hotfix and has never done it before with this world size. it is a multiplayer server which i have a lot of people on, and i cannot load it up for longer then 10 seconds. this is very annoying for everyone waiting. i have deleted minecraft once and reinstalled it, didnt change and i also deleted half my worlds and still nothing.