Entering the Nether crashes our clients

Hello, I have recently brought a server and It is running the Yogscasts complete mod pack I have also Installed Bukkit and some plugins I thought everything was running nice, However, Myself and other players have discovered a major problem, After you have made a Nether portal and then try to go through Into the Nether It just simply close our clients do the desktop no warnings or anything just a straight close. What could cause this?

I am Hosting with Nitrous Networks.

Here are the things I have running on the Server:

Bukkit 1.6.4
Yogscast complete 2.9.3.1


PLUGINS:
BOSEconomy
BanItem
BookMailbox
ButtonWarp
Buycraft
EnjinMinecraftPlugin
Essentials
EssentialsAntiBuild
EssentialsChat
EssentialsProtect
EssentialsSpawn
GAListener
GriefPrevention
ItemCase
ItemRestrict
LinksOnSigns
Lockette
MCBans
Morpheus
Multiverse-Core
Multiverse-Inventoies
Multivers-Portals
PermissionsEX
SurvivalGames
SurvivalSigns
TreeAssist
Vault
Votifier
WorldEdit
WorldGuard
Prism
Any help would be great.

 

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