When a client tries to connect, he gets a HOST_ERROR: Unexpected authentification protocol

The problem started today, the exact error is as follows:

Host_Error: Unexepected authentication protocol 220205841!

The number changes almost everytime tho. Me and Towelie have no idea what is causing this error, it happens to everyone who tries to connect. We really can’t afford this error, because many players would be dissapointed…

Thanks in advance.

http://www.facepunch.com/threads/1019709-Cannot-connect-to-dedi-after-update?p=25692098&viewfull=1#post25692098

Thank you Chris, much appreciated!