Extreme lag, very localized, out of nowhere.

Hi all,

My server was running great for months, but suddenly everyone gets EXTREME fps lag around my spawn.

If you are outside that region or in the nether/creative world there is no problem at all, but if you come within a ~40 block radius of my spawn people get horrible lag ( I usually run at 150 fps, but it drops to 1).
I was there when it happened, we were digging out an underground complex with 4 people together, and BOOM, it hit us.
I restarted the server, thinking it was server wide, didn't work, heard from others they had no lag at all, so I tp'd away from spawn, and everything was fine again.


Does anyone have an idea what this is? and more important, how to fix it?
I never encountered anything like this before (I've been running this server since beta 1.2).

OS: WinServer 2008
CB: 1337
Plugins: didn't change a thing the last week, but here goes: BlueTelePads, Bookworm, boosCooldown, PEX, chatmanager, modifyworld, permissions (bridge), WorldEdit, WorldGuard, Commandbook, Factions, iConomy, Localshops, HeroicDeath, Logblock, mcMMO, mobbounty, MultiInv, Nethrar, NoCheat, PreciousStones, Spout, Vault, WorldBorder, OtCO