Changes to the MythTV communications protocol require a change to the protocol version. This is most commonly noticed when running different versions of a backend and frontend. MythTV does not support running different protocol versions between a client and server.
If you experience a protocol mismatch, you need to be sure all your systems are running the same version of the software. If you are using a development branch like trunk or the fixes branch, be sure your systems are all running the same revision of the software as the protocol version can change within a development branch before an official release tarball is made.