Seems like a corrupted or stale download for that macOS update.
Apple Remote Desktop Client free download - Microsoft Remote Desktop, Remote Desktop Manager, Apple iTunes, and many more programs. You can use the Remote Desktop client for Windows Desktop to access Windows apps and desktops remotely from a different Windows device. This documentation is not for the Remote Desktop Connection (MSTSC) client that ships with Windows. It's for the new Remote Desktop (MSRDC) client. Download Apple Remote Desktop Client for Mac to remote control to manage Macs. Download the Microsoft Remote Desktop client from the Mac App Store. Set up your PC to accept remote connections. (If you skip this step, you can't connect to your PC.) Add a Remote Desktop connection or a remote resource. You use a connection to connect directly to a Windows PC and a remote resource to use a RemoteApp program, session-based.
What I usually do to try to resolve those.... Log out of the Mac App Store and then log into the Mac App Store again, and try the download again. Or log out of the Mac App Store, reboot the Mac, and try the download again. Or log out, reboot into safe mode, then reboot normally, and try again. Apple has some App Store troubleshooting information, though I've usually found logging out of the Mac App Store and rebooting about as far as I've needed to go to get a Mac App Store download to work again.
If all that fails and if you have add-on monitoring or anti-malware or performance- or cache-optimizing tools installed on your system, test whether those are involved and remove those per the providers' directions, and try the install again.
Worst case, reload the combo update for macOS Sierra 10.12.6 and try again. The combo update, not the delta update. That reinstallation should not effect your system, or your saved data, but will reset your macOS environment back to what 10.12.6 should look like, less any subsequent patches.
I'd also ensure you have and keep current backups of your data, as macOS crashes can be caused by hardware problems. Reinstalling doesn't fix flaky or failing hardware.
(This whole area and how the pieces fit together can get somewhat confusing, too. I know this stuff puzzled me when I first met up with this, too. What you're encountering a problem with macOS and the Mac App Store downloads, and is not specific to the Apple Remote Desktop package that Apple sells. Both macOS Screen Sharing and Apple Remote Desktop product use that screen sharing client you're having issues installing. That client is an integral part of macOS, and not something that can be removed. And something that should not be balking when trying to install the macOS update, either.)
Sep 20, 2017 1:37 PM