[[Server Help] Server not working after host pc is turned off]

I have been running a Tekkit server for me and my friend to play on together from my home PC, except after I restart my computer or turn it on, neither him or myself can join the server. So far the only way to fix this problem is to generate a fresh world, but I would like to find a way around it. So far it has happened twice.

When I run the server after my computer has been off I am greeted with this lengthy error message: (I have no idea what this means)

2014-01-12 13:34:18 [sEVERE] [ForgeModLoader] A fatal exception occurred during

the server starting event

java.lang.NullPointerException

at universalelectricity.prefab.flag.ModFlag.readFromNBT(ModFlag.java:34)

at universalelectricity.prefab.flag.ModFlag.<init>(ModFlag.java:27)

at atomicscience.ZhuYao.serverStarting(ZhuYao.java:719)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at cpw.mods.fml.common.FMLModContainer.handleModStateEvent(FMLModContain

er.java:494)

at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java

:74)

at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(Synch

ronizedEventHandler.java:45)

at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)

at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.jav

a:296)

at com.google.common.eventbus.EventBus.post(EventBus.java:267)

at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadContro

ller.java:192)

at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadControll

er.java:172)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java

:74)

at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(Synch

ronizedEventHandler.java:45)

at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)

at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.jav

a:296)

at com.google.common.eventbus.EventBus.post(EventBus.java:267)

at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadControl

ler.java:103)

at cpw.mods.fml.common.Loader.serverStarting(Loader.java:740)

at cpw.mods.fml.common.FMLCommonHandler.handleServerStarting(FMLCommonHa

ndler.java:314)

at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(Dedicated

Server.java:205)

at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:431)

at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)