22:29:20 [SEVERE] [VANISH] A flaw has been caught. Please report this (it wont break things) :) .
java.lang.ClassCastException: net.minecraft.server.Packet21PickupSpawn cannot be cast to net.minecraft.server.Packet28EntityVelocity
at to.joe.vanish.sniffers.Sniffer28EntityVelocity.checkPakkit(Sniffer28EntityVelocity.java:19)
at to.joe.vanish.sniffers.Sniffer.checkPacket(Sniffer.java:20)
at org.getspout.spout.packet.listener.PacketListeners.canSend(PacketListeners.java:72)
at org.getspout.spout.SpoutNetServerHandler.syncedSendPacket(SpoutNetServerHandler.java:620)
at org.getspout.spout.SpoutNetServerHandler.syncFlushPacketQueue(SpoutNetServerHandler.java:611)
at org.getspout.spout.SpoutNetServerHandler.queueOutputPacket(SpoutNetServerHandler.java:570)
at org.getspout.spout.SpoutNetServerHandler.sendPacket(SpoutNetServerHandler.java:555)
at net.minecraft.server.NetServerHandler.disconnect(NetServerHandler.java:118)
at org.getspout.spout.SpoutNetServerHandler.disconnect(SpoutNetServerHandler.java:596)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:450)
at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:211)
at net.minecraft.server.Packet14BlockDig.a(SourceFile:43)
at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:93)
at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:586)
at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:527)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)

Thanks for the report! Can you run this command in console and paste the result:
/version Spout

Assuming that after this period of time you've resolved the issue