I originally posted this on July 18, 2020:
I have 4 computers on a peer-to-peer network. Two of the PCs can log into any PC on the network using Remote Desktop Connection while the other two cannot log into any of them. The two that cannot log into any other computer, displays the error message below. I have looked at group policies, registry values and some other settings and I cannot find why two work and two do not.
see https://answers.microsoft.com/en-us/windows/forum/all/remote-desktop-connection-issue/0a065e30-0140-4125-88c8-381cc63d17e7 for original post. I could respond to the original as it is now locked.
I finally figured out the issue. The cause was Bitdefender Free blocking RDP on the client computer. Disabling Bitdefender confirmed it. Although all my computers were using it, Bitdefender was only blocking it for some PCs. Removing Bitdefender and using Windows Defender resolved the issue. The error message give no clue that this can be a firewall issue. I recommend Microsoft modify the error message or provide a new one that mentions a firewall issue as a possible cause.