It is good to know that SSH 1 works. This output
SSH Enabled - version 1.99
usually indicates that the device will accept both SSH 1 and SSH 2. So I am puzzled why SSH 2 is not working. In the original post you tell us "complains to generate 768-bit key when I try to activate SSH 2". I am not sure what that is about. Can you tell us what modulus was used to generate the SSH/RSA keys?
What happens if you generate new SSH/RSA keys and specify modulus 2048?