FTB unleashed server crash

[powerwizzardz]

hi,
my ftb server won't generate the world
it stops when it starts to generates the world and gives this report:

2013-08-29 12:12:22 [INFO] [Minecraft-Server] Preparing level "world"
2013-08-29 12:12:30 [INFO] [STDERR] java.lang.VerifyError: (class: net/minecraft/util/ReportedException, method: func_71575_a signature: ()Lnet/minecraft/crash/CrashReport Illegal constant pool index
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.world.World.<init>(World.java:312)
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.world.WorldServer.<init>(WorldServer.java:107)
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.server.MinecraftServer.func_71247_a(MinecraftServer.java:238)
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:186)
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:431)
2013-08-29 12:12:30 [INFO] [STDERR] at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
2013-08-29 12:12:32 [INFO] [Minecraft-Server] Stopping server
2013-08-29 12:12:32 [INFO] [Minecraft-Server] Saving players
2013-08-29 12:12:32 [INFO] [STDERR] java.net.SocketException: Socket closed
2013-08-29 12:12:32 [INFO] [Minecraft-Server] Saving worlds

please help me
thanks