It appears that the user account you’re currently using doesn’t have sufficient permissions to run that command. The root user has full access to all functions, while the admin user operates with limited rights — including restrictions on executing SSH commands. Please try logging in as root, and you should be able to run the command without issues.
Additionally, unless you have a specific requirement for staying on your current firmware version, I would highly recommend updating to the latest stable release to ensure better performance, security, and compatibility.