Lag when OPs join the server.

I am getting alot of issues when ops join the server its tends to lag. There isn't any plugin involvement because I tried this without any plugins and it still lagged. Any help?

 

What are the specs of the hardware you are running your server on?

 

Moved to Bukkit Help.

 

same problem here... I'm using GroupMan without '*'-nodes (these cause lags too)
hardware: cpuinfo, 4 gb ram, broadband-connection (vps)
plugins:

GroupManager, WorldEdit, WorldInventories, Vault, Multiverse-Core, ecoCreature, WorldGuard, MineBackup, iConomy, Permissions, HawkEye, frdmn-cmd, BKCommonLib, NoCheat, NoLaggChunks, Essentials, WorldBorder, NoLaggLighting, NoLaggItemBuffer, NoLaggTNT, EssentialsProtect, EssentialsSpawn, Multiverse-Portals, LWC, dynmap, Dynmap-WorldGuard, NoLagg, EssentialsChat, JSONAPI​

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I'm on the 1.2.3 beta build with latest Essentials