Ok if your like me and Updated before checking the NGU server yo will get this error, that error means you are using the wrong client version the NGU server.
You need to downgrade / rollback to the previous version. In the future, do not update to the newest version before trying to connect to the server.
Download previous version: You must login or register to view this content. (This is the previous.jar file)
How to downgrade (for Windows):
1. Hit the Start button. Click inside the white search box.
2. Type: %AppData%\.minecraft\bin
3. A folder will open.
4. Copy over the minecraft.jar from the download above into the folder that just opened, and overwrite the existing file.
5. Now you can play! Go run the Minecraft.exe file that you normally do.
Yeah, he's doing it now. I was working on my house and he shut down the server. +1 for update. -1 for missing plugins No OB = all my protected blocks are unprotected = ..