Same bug as listed in Minecraft MC-34686 ...
12:57:09 PM CONSOLE: [INFO] cosmicWavez [/68.230.61.253:40908] lost connection: Internal Exception: io.netty.handler.codec.DecoderException: java.io.IOException: Bad packet id 81
12:57:28 PM CONSOLE: [INFO] cosmicWavez [/68.230.61.253:38173] lost connection: Internal Exception: io.netty.handler.codec.DecoderException: java.io.IOException: Bad packet id 11508
etc etc for the different players including myself trying to get onto my own server.
Comments

Is this still a concern in the latest Minecraft version 13w48b? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
This ticket is invalid without the requested information, no response has been received within a reasonable time and we are assuming the issue has been resolved. If you are still experiencing this issue, we can reopen it at your request.
Affects 13w42b unf as well