I've been having this problem with VF4 VanillaCraft, and decided to try it on another server... turns out it's an issue with every server I've tried to join. When i play on singleplayer (survival and creative), I have no issues. As soon as I get on multiplayer, it won't even load ten blocks ahead of me without crashing. VF4 VanillaCraft worked for a few seconds, and as soon as I got on the south rail, it crashed. Every time I try to rejoin, it crashes right on the spot. Any solutions/temporary help until I can find a more permanent solution?
Update your java and lwjgl files? That's resolved most weird stuff I've seen to date. http://www.minecraftwiki.net/wiki/Tutorials/Update_LWJGL