Cant Update Posts

Hi

I cant update any of my posts on one of my sites! I noticed the error in version 3.0 so i updated to 3.01 and i still have the same issue. Basically if i update my post, i’m getting the post updated message as usual, however the big box where you write in reverts back to how it was and the post simply does not update.

I’ve tried disabling all plugins and the same thing is happening. What can i do to fix this? Cheers.