Q: Apple Remote Desktop Admin 3.8 Update

This update (1.1 and earlier currently) breaks screen sharing on OSX computers other than Yosemite.  There is a bug in the software update.

They should have only updated Yosemite computers and not those still running earlier OSX versions. 

There is an explanation on how to downgrade to 3.7 in another thread by UM-LinuxGuru:

"UM-LinuxGuruMar 24, 2015 1:09 PM Re: mavericks messages not screen sharing
Re: mavericks messages not screen sharingin response to David Vrooman

I happened to stumble across this issue. I loaded a test machine with a Mavericks 10.9.0 installer, then selected upgrades to see what would break it. It is RDC Update 3.8.2 v1.1. After spending time with AppleCare, they told me I might see a fix in a week. Right. I need a fix right now.

So, I used my 15 years of Linux diagnostic skills, and came up with a quick fix, which I will test further. I downloaded Apple Remote Desktop 3.7 Client . If you try to install it now, it will say, "Can't, newer already installed." Fine. goto /Library/CoreServices/, archive RemoteManagement, then put RemoteManagement in the trash (as admin), and empty the trash. Now run the 3.7 installer. I now have screen sharing again, while I wait for Apple's fix.

I will test updates 3.7.1 and 3.7.2 if I can find them."

Robert had a correction to this instruction:

"One correction: the path to the Remote Management folder is: /System/Library/CoreServices/  (not /Library/CoreServices/)"

The ARD client 3.7 solves screen sharing problems on non-Yosemite computers until they make the upgrade.