Server stops all time

My server keep timing out and idk why. I have 1,5GB ram and the regular ram usage is about 700-900MB ram. But almost all time I get this in console and the server dies.
McMyAdmin, build 1337 and I use these plugins

Code:

2011-11-03 12:40:18 [WARNING] Can't keep up! Did the system time change, or is the server overloaded?
2011-11-03 12:40:26 [SEVERE] java.util.ConcurrentModificationException
2011-11-03 12:40:26 [SEVERE] at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
2011-11-03 12:40:26 [SEVERE] at java.util.ArrayList$Itr.next(Unknown Source)
2011-11-03 12:40:26 [SEVERE] at net.minecraft.server.World.tickEntities(World.java:1109)
2011-11-03 12:40:26 [SEVERE] at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:467)
2011-11-03 12:40:26 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
2011-11-03 12:40:26 [SEVERE] at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)
2011-11-03 12:40:26 [SEVERE] Unexpected exception
java.util.ConcurrentModificationException
 at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
 at java.util.ArrayList$Itr.next(Unknown Source)
 at net.minecraft.server.World.tickEntities(World.java:1109)
 at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:467)
 at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
 at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)

 

Do what the big RED bar above your post says.

 

sry thank you

I dont know all cause Im not the host.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

Ask the host then.

 

Ive tried editing my post but nothing happend... And I have sended a mail to the host now