Well there is a fix withc allow you to play Alpha version
and if you do that you are able to play on the server
but server will be updated when the new hey0 comes out.
To use this you need to:-
1. Make sure your Minecraft is up to date (the beta version at this time).
2. Open an Explorer Window (Win Key + E) change to the minecraft directory
"%APPDATA%\.minecraft\bin", you can do this by pasting it into the address bar (without the quotes)
3. Delete everything except the version file, this is what minecraft checks to make sure the client is up to date.
4. Download this file and extract the contents of the zip to into the bin folder above.
Download File Link: http://www.fileplay.net/channel....servers
Now you have your Alpha files, and your correct version file, which means.. you can now play again!
Just load up MC login as usual and connect up to your MC server, and voila.