Thank you for your message.
Could you please tell us the operating systems you are using and their exact versions, and also the exact versions of TeamViewer that are installed on your devices?
Main: Mac OS Sierra 10.12.6 Team Viewer Version 14.3.4730Remote: Windows 10 Team Viewer Version 14.3.4730
I've tried the Remote on Numerous Different Versions of Windows inlucding WIndows 7, and 8 as well as all versions of windows 10. None of them work and all give the same error. The weird thing is if I choose Remote Control using windows authentication and enter the Windows user name and password I am able to connect just fine.
I replied to your post here: Mac to PC Remote Computer "Unable To Connect Reason Unknown" Partner Still using an older version of TeamViewer
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