Mac Joining my FTB vanilla server, crash/bug? " Internal Server Error.

[Giantpotato]

Whenever I try and join my FTB server, I log on and for a few seconds, then I get "kicked" from the server. When this happens, the disconnected message says " Internal Server Error". Can someone, ANYONE please fix this.
Here is what it said the server console:

[INFO] User giantpotato connecting with mods [XyCraft, ThermalExpansion, RedPowerWiring, BuildCraft|Silicon, ThermalExpansion|NEI, ThermalExpansion|Transport, TwilightForest, OmniTools, BuildCraft|Transport, GraviSuite, IC2NuclearControl, BuildCraft|Core, ThermalExpansion|Factory, RedPowerCompat, RedPowerLogic, ObsidiPlates, IC2, ThermalExpansion|Energy, ExtraBees, StevesCarts, drceph.petrogen, Thaumcraft, ExtrabiomesXL, TC, Forestry, ComputerCraft, BinnieCore, AdvancedMachines, AdvancedSolarPanel, BuildCraft|Factory, RedPowerMachine, IronChest, BuildCraft|Energy, Railcraft, GregTech_Addon, SoulShards, RedPowerCore, MiscPeripherals, PortalGun, CCTurtle, ModularForceFieldSystem, factorization, RedPowerControl, RedPowerLighting, RedPowerBase, RedPowerWorld, BuildCraft|Builders]
[INFO] giantpotato[/74.89.148.113:38967] logged in with entity id 218 at (-921.1555926298403, 64.0, 660.6999999880791)
[WARNING] Failed to handle packet for giantpotato/74.89.148.113: java.lang.ClassCastException: su cannot be cast to thaumcraft.api.IVisRepairable
java.lang.ClassCastException: su cannot be cast to thaumcraft.api.IVisRepairable
at thaumcraft.common.EventHandler.livingTick(EventHandler.java:243)
at net.minecraftforge.event.ASMEventHandler_83_EventHandler_livingTick_LivingUpdateEvent.invoke(.dynamic)
at net.minecraftforge.event.ASMEventHandler.invoke(ASMEventHandler.java:35)
at net.minecraftforge.event.EventBus.post(EventBus.java:103)
at net.minecraftforge.common.ForgeHooks.onLivingUpdate(ForgeHooks.java:333)
at md.j_(EntityLiving.java:803)
at qx.j_(EntityPlayer.java:328)
at iq.g(EntityPlayerMP.java:286)
at iv.a(NetServerHandler.java:310)
at eb.a(SourceFile:136)
at cg.b(TcpConnection.java:458)
at iv.d(NetServerHandler.java:136)
at iw.b(NetworkListenThread.java:57)
at ht.b(SourceFile:30)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:703)
at ho.r(DedicatedServer.java:269)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:599)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
at fy.run(SourceFile:849)

 

[Ashzification]

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[Schwen]

Whenever I try and join my FTB server, I log on and for a few seconds, then I get "kicked" from the server. When this happens, the disconnected message says " Internal Server Error". Can someone, ANYONE please fix this.
Here is what it said the server console:

[WARNING] Failed to handle packet for giantpotato/74.89.148.113: java.lang.ClassCastException: su cannot be cast to thaumcraft.api.IVisRepairable
java.lang.ClassCastException: su cannot be cast to thaumcraft.api.IVisRepairable
...

Same thing happened to me and I narrowed it down to my enchanted diamond armor (enchanted with X-key as Op). It was no problem to equip the enchanted armor, but after I took the first hit from a mob, the game began to crash with exact same error. It disappeared though when I deleted my armor. I don't know which attribute is responsible but should be fairly easy to figure out (based on the error, it looks like it has something to do with a repair-attribute).