2.3 Dev? I'm not a coder, but I'd imagine that if you were trying to play multiplayer with a Development snapshot, SVN, pre-built, or otherwise, that it would *not* be compatible with a stable release server, given the substantial changes in 2.3 since 2.2.1 was released. I could be wrong, but I think you would need to have another player or server running the exact same build version for it to have any chance of working.
Assuming I'm correct, and I heard you right, I would recommend using only a stable release (one from the sourceforge download page) for multiplayer.