Minecraft troubleshooting
From Aporkalypse Wiki
Client/Server Version Errors
The Aporkalypse server can only be updated once the plug-ins required by the server are also updated by their respective developers. For this reason, the server often runs one or two versions behind the most current release. If you are unable to log in to the server due to version incompatibility, you will need to change the version of your client. While you can perform the version downgrade manually, most players will find it easier to use one of the solutions below. Bear in mind that this page may not be the most current source of information, and you are encouraged to ask on the MeFight Club forums or Minecraft forums if these solutions do not work for you.
- Minecraft Version Changer (this app is handy because it will download the version of the minecraft.jar that you need)
- MagicLauncher (you will need to locate the correct version of minecraft.jar manually)