Apple Remote Desktop or another administration application is currently running.

Have you ever encountered this message:

«Apple Remote Desktop or another administration application is currently running.»
This message shows up when you try to observe or control a Mac that is itself running 'Remote Desktop Admin'.

If you have access via ssh, you can try this:


connect to the client via ssh
enter these commands:

defaults write /Library/Preferences/com.apple.RemoteManagement AdminConsoleAllowsRemoteControl -bool true
sudo killall 'Remote Desktop'

From now on, you are able to access this client even though Remote Desktop Admin is running. 

I know you can adjust this setting in the preferences.

But, if you are not able to adjust them, do it via ssh.