This error is often caused when the SonicWall device refuses the connection from the Liongard agent.
To resolve, remotely connect into the Agent server and attempt to access the SonicWall device via the IP:PORT in the error code. Resolve any errors that occur.
Please note that depending on the version of the SonicWall, you will need to access the device with different methods:
V6 - SSH
V7 - HTTPS