Remote user is gone, not running Shutdown Manager anymore, remote Shutdown Manager server was stopped or there is a network problem. Check remote Shutdown Manager's Server Security settings in Options and Preferences, and verify the valid IP list is ok, it means, it contains an IP definition and is valid for your computer.
Example:
If your computer's IP is 192.168.0.3 and you want to grant access to any computer on your local network, you may define, on Security settings in Options and Preferences of remote Shutdown Manager, the "global" IP definition 192.168.0.