you should check the output of the ssh client run in verbose mode:
If that does not provide enough information you should check the logs on the machine where sshd is running. The exact file to check will depend on your setup/distribution, but on a Debian based machine it would be /var/log/auth.log
Please check this file for the entries corresponding to the failed ssh attempt: this should help you understand what is causing the problem. If you still can't work it out please post the relevant lines from the log file and the output of 'ssh -vvv' in [code] tags on the forum.