Q: Can't control a Mac with OSX 10.11 from my Remote Desktop Admin 3.8

On the remote mac that was updated, go to System Preferences -> Sharing. Try toggling the box for Remote Management off and on again.

I am having the exact same issue.  Running 3.8 admin, cannot connect to a client on 3.8.5.  Am able to connect to a client running 3.8.4 however without any issue.

I am having the same problem.  Problem started when client was 3.8.4.  Upgraded to 3.8.5, which fixed the problem for about 10 minutes.  Now have the same problem.  I suspect a preference file, but can't figure out which one.

I was attempting to access a server.  Turns out that the Server app now has an "access" menu under the Server details.  Among other things, this access menu allows you to restrict access to certain services for security, including screen sharing.  Mine was set to "only this Mac" by default.  When set to the network and administrator access, ARD become operative again.