This Knowledgebase article explains the dependency of the Start Group feature on the 'Server' service and the Neverfail for File Server Plug-in.
The Start Group feature fails to restart the passive server(s) after the Neverfail for File Server Plug-in is uninstalled.
After uninstalling the Neverfail for File Server Plug-in, the Start Group menu item remains available on the System Tray, but selecting Start Group generates the following error message:
Error Starting Neverfail Heartbeat Group: An error occurred accessing the Service Control Manager for the Secondary Server. The error was: The RPC server is unavailable.
The Start Group feature requires the 'Server' service to be running on all servers in the group to start Neverfail successfully on all servers. The 'Server' service is managed by Neverfail for File Server. If the Neverfail for File Server Plug-in is uninstalled, the 'Server' service does not restart on the passive server(s) and therefore cannot respond to Start Group. This can be true even after the Neverfail for File Server plug-in is reinstalled.
Manually restart the 'Server' service on all servers to resolve the error.
Neverfail Heartbeat V6.0
Neverfail for File Server Plug-in