IMPORTANT THING TO REMEMBER WHEN YOU REINSTALL ARD ON YOUR SERVER:  Be sure to go to the ‘Preferences’ pull-down in ARD and set ARD so you can log into the machine when ARD is up and running.

This is the path to follow. In your finder menu,  ARD > Preferences > Security > “Allow control of this computer when this application is running”

Another one you may want to check is under ‘General’,  Double - Clicking a computer performs “control”.