Unable to spawn blocks

[Grandsatsuma]

I have a rental server for about 15 people, I had tekkit working fine back in 2.0 but now 2.1 doesn't let anyone spawn blocks, there is no tekkit noises and no tekkit blocks spawn on the map, if I try to spawn a block i get a java error and my client is kicked.

The message on my client is:

Internal exception: Java.net.SocketException: Software caused connection about: recv failed

This is what it says in the console at the moment of spawning a block.

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16:40:35 [iNFO] grandsatsuma has disconnected, reason: disconnect.genericReason

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.NetworkReaderThread.run(SourceFile:76)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.NetworkManager.c(NetworkManager.java:270)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.NetworkManager.h(NetworkManager.java:152)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.Packet.a(Packet.java:79)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.Packet107SetCreativeSlot.a(SourceFile:25)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] at net.minecraft.server.Packet.b(Packet.java:151)

25.03 16:40:35 [server] INFO >

16:40:35 [sEVERE] java.lang.NullPointerException

25.03 16:40:32 [server] INFO >

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