Crashes every 5-10 hours

Code:

2011-05-02 18:09:11 [SEVERE] java.util.ConcurrentModificationException
2011-05-02 18:09:11 [SEVERE]     at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
2011-05-02 18:09:11 [SEVERE]     at java.util.AbstractList$Itr.next(AbstractList.java:343)
2011-05-02 18:09:11 [SEVERE]     at java.util.AbstractCollection.removeAll(AbstractCollection.java:336)
2011-05-02 18:09:11 [SEVERE]     at net.minecraft.server.World.cleanUp(World.java:934)
2011-05-02 18:09:11 [SEVERE]     at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:367)
2011-05-02 18:09:11 [SEVERE]     at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:285)
2011-05-02 18:09:11 [SEVERE]     at net.minecraft.server.ThreadServerApplication.run(SourceFile:394)
2011-05-02 18:09:11 [SEVERE] Unexpected exception
java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
    at java.util.AbstractList$Itr.next(AbstractList.java:343)
    at java.util.AbstractCollection.removeAll(AbstractCollection.java:336)
    at net.minecraft.server.World.cleanUp(World.java:934)
    at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:367)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:285)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:394)

This is what I got the second last time.

Now I get out of memory errors every 5-10 hours. I have given the server 2,5GB of RAM (and we usually have about 10 players online).. and I have about 20-25 plugins enabled .

What is causing dis?

 

One of your plugins is causing "dis" - start working on removing them until you find your culprit.