OpenSSH 4.2p1/Maverick interoprability

Hi there. I have run in to a bit of a problem trying to connect a custom-built client using Maverick J2SSH to an OpenSSH 4.2p1 server. I am getting "Bad packet length" errors on the server when I attempt a SSH2 client connection. Reverting to SSH1 always seems to work.

Any help? Obviously, I am not too experienced with this yet.