Crash on Server

[Gamephantom]

I installed the mod on the server. So i want to play on the server, which already had an world and Tinkers Construct installed. When i have the mod installed on the server, the client crash with this error code

---- Minecraft Crash Report ---- // There are four lights!

Time: 23.11.15 22:28 Description: Rendering item

java.lang.NullPointerException: Rendering item at tconstruct.library.weaponry.BowBaseAmmo.getDefaultColor(BowBaseAmmo.java:169) at tconstruct.library.tools.ToolCore.getCorrectColor(ToolCore.java:684) at tconstruct.library.tools.ToolCore.func_82790_a(ToolCore.java:662) at net.minecraftforge.client.ForgeHooksClient.renderInventoryItem(ForgeHooksClient.java:195) at net.minecraft.client.renderer.entity.RenderItem.func_82406_b(RenderItem.java:563) at net.minecraft.client.gui.GuiIngame.func_73832_a(GuiIngame.java:955) at net.minecraftforge.client.GuiIngameForge.renderHotbar(GuiIngameForge.java:206) at net.minecraftforge.client.GuiIngameForge.func_73830_a(GuiIngameForge.java:141) at net.minecraft.client.renderer.EntityRenderer.func_78480_b(EntityRenderer.java:1328) at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1001) at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:898) at net.minecraft.client.main.Main.main(SourceFile:148) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:483) at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

But if i remove the mod from the client and server, everything is normal...