The problem may be related to the potentially incompatible changes introduced in OpenSSH 6.7  (included in Copssh 5 and higher) to remove unsafe algorithms.

• If you run Copssh 5.8.1 or higher, you can update the configuration via GUI: Copssh Control Panel - Configuration - Advanced - HostKeyAlgorithms or alternatively, you can add following line to the section of the configuration file control/bin/copsshcp.config:

HostKeyAlgorithms=+ssh-rsa,ssh-dss

• Restart the service via Copssh Control Panel