Apple recently issued a minor bug fix upgrade for Apple Remote Desktop (client and server portions). MPG recommends caution in upgrading ARD for this update.
With the usual Apple Core Rot software incompetence, the “upgrade” destroyed my ability to get to one server, made getting to a 2nd server flaky, and the 3rd server has lucked out somehow—but I suspect problems will crop up just when I need to use ARD, a scary thought. But there seems to be a fix, see further below.
For the problem server on 10.8, I rebooted twice and reinstalled the latest applicable client—no go, that server is now unreachable. The built-in firewall is disabled. Searching the web, I see that Apple has been breaking things like this for some years now—pure incompetence.
This is stuff that until the update has worked for 7 years. The nitwits at Apple seem to think everyone runs only the latest OS; my servers run 10.8, 10.10, and 10.11. Apple does not respect its users enough to actually test its “upgrades”, a pattern worsening year by year.
Update: my iMac with Apple Remote Desktop 3.8 works fine with the problem server. But as soon as I updated to Apple Remote Desktop 3.9, the iMac also fails to be able to connect. Clearly Apple has BROKEN Apple Remote Desktop 3.9.
Update 2: the user comments on the App Store confirm these problems in spades.
The fix — check a box
Found by scanning the numerous complaints. Why does Apple Remote Desktop make no effort to warn of older clients and inform the user of this change, rather than mysteriously hanging on any/all attempts to connect? ARD darn well knows the OS version from the configuration and/or prior connection. Two hours of my time wasted due to Apple’s contemptible contempt for its users.
The weird thing is that this fix was not needed for one of the servers also running 10.8. It suggests yet more bugs.