[Urgent] Server Crashes Every 20-30 Min. !~

Hello, SX here, I currently run a CraftBukkit server version 1.7.2 on Ubuntu Linux. Everything is running smooth except... every 30 minuets or so, the whole server gets lag and all are disconnected and it takes about 10 minuets just to log back in. Here is a log of when it happens and a plugins list:
Log: http://pastebin.com/29E0VrQ6
Plugins: http://pastebin.com/BBT56DdQ

I would feedback ASAP If you can help, kudos to you! Please respond =(
-SX

Edit:
This is very new!

Encountered an unexpected exception

net.minecraft.server.v1_7_R1.ReportedException: Ticking entity
> at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:637) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.DedicatedServer.u(DedicatedServer.java:250) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.MinecraftServer.t(MinecraftServer.java:541) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:453) [craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
Caused by: java.lang.IllegalArgumentException: n must be positive
> at java.util.Random.nextInt(Random.java:300) ~[?:1.7.0_25]
> at net.minecraft.server.v1_7_R1.EntitySpider.dropDeathLoot(EntitySpider.java:113) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.EntityLiving.die(EntityLiving.java:776) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.EntityLiving.damageEntity(EntityLiving.java:725) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.EntityMonster.damageEntity(EntityMonster.java:47) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.EntityArrow.h(EntityArrow.java:228) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.World.entityJoinedWorld(World.java:1332) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.World.playerJoinedWorld(World.java:1313) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.World.tickEntities(World.java:1201) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.WorldServer.tickEntities(WorldServer.java:480) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:633) ~[craftbukkit.jar:git-Bukkit-1.6.4-R2.0-19-gcb772e9-b2936jnks]
> ... 4 more
[13:09:41 ERROR]: This crash report has been saved to: /home/kobek/Desktop/EC/./crash-reports/crash-2014-03-23_13.09.41-server.txt
>

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

 

Can you get the error log from your crash reports folder?

 

http://pastebin.com/Zw0Je84m