2011-12-13 05:43:24 [SEVERE] java.lang.ClassCastException: net.minecraft.server.Packet50PreChunk cannot be cast to net.minecraft.server.Packet28EntityVelocity
2011-12-13 05:43:24 [SEVERE] at to.joe.vanish.sniffers.Sniffer28EntityVelocity.checkPacket(Sniffer28EntityVelocity.java:22)
2011-12-13 05:43:24 [SEVERE] at org.getspout.spout.packet.listener.PacketListeners.canSend(PacketListeners.java:70)
2011-12-13 05:43:24 [SEVERE] at org.getspout.spout.SpoutNetServerHandler.syncedSendPacket(SpoutNetServerHandler.java:584)
2011-12-13 05:43:24 [SEVERE] at org.getspout.spout.SpoutNetServerHandler.syncFlushPacketQueue(SpoutNetServerHandler.java:575)
2011-12-13 05:43:24 [SEVERE] at org.getspout.spout.SpoutNetServerHandler.queueOutputPacket(SpoutNetServerHandler.java:534)
2011-12-13 05:43:24 [SEVERE] at org.getspout.spout.SpoutNetServerHandler.sendPacket(SpoutNetServerHandler.java:519)
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.EntityTrackerEntry.a(EntityTrackerEntry.java:162)
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.EntityTrackerEntry.track(EntityTrackerEntry.java:103)
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.EntityTracker.updatePlayers(EntityTracker.java:130)
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:532)
2011-12-13 05:43:24 [INFO] [MCBans] viestursi has disconnected!
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
2011-12-13 05:43:24 [SEVERE] at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)
2011-12-13 05:43:24 [SEVERE] Unexpected exception
java.lang.ClassCastException: net.minecraft.server.Packet50PreChunk cannot be cast to net.minecraft.server.Packet28EntityVelocity
at to.joe.vanish.sniffers.Sniffer28EntityVelocity.checkPacket(Sniffer28EntityVelocity.java:22)
at org.getspout.spout.packet.listener.PacketListeners.canSend(PacketListeners.java:70)
at org.getspout.spout.SpoutNetServerHandler.syncedSendPacket(SpoutNetServerHandler.java:584)
at org.getspout.spout.SpoutNetServerHandler.syncFlushPacketQueue(SpoutNetServerHandler.java:575)
at org.getspout.spout.SpoutNetServerHandler.queueOutputPacket(SpoutNetServerHandler.java:534)
at org.getspout.spout.SpoutNetServerHandler.sendPacket(SpoutNetServerHandler.java:519)
at net.minecraft.server.EntityTrackerEntry.a(EntityTrackerEntry.java:162)
at net.minecraft.server.EntityTrackerEntry.track(EntityTrackerEntry.java:103)
at net.minecraft.server.EntityTracker.updatePlayers(EntityTracker.java:130)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:532)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)

Looks like spout broke. Make sure you're running the latest CB build and latest Spout build.