ARDAgent not open anymore

Three computers in same remote location. Mini server running 10.12.6 that I can manage via Apple Remote Desktop (3.9). A client mini running 10.13.3 and a Mac book pro also 10.13.3 both of which are showing up in the computers list on the managing computer but without ARD version. When I go to System/library/core services/remote management and click on the ARDAgent app I am greeted with the subject message. Tried Force quitting and rebooting to no avail. I can connect to the server and from there, through screen sharing, administer both rogue computers, but, I would like to do without this step (slower response and I have to admin one at a time)

Suggestions, pppleeease.