I'm in the process of setting up a new Hyper-V server, and for some reason I was unable to connect via Terminal Services to the server... I had properly enabled the "Allow connections from computer running any version of Remote Desktop (less secure) option".  However, no matter, what I did, I got the following error:

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Remote Desktop Disconnected

Remote Desktop cannot connect to the remote computer because the authentication certificate received from the remote computer is expired or invalid.
In some cases, this error might also be caused by a large time discrepancy between the client and server computers.

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It turns out that the message was actually correct.  Although my time was correct, and it was the "22nd" on both computers, they were off by exactly a month.  One thought that it was 2:50 PM on June 22nd, and the other thought it was 2:50 PM on July 22nd. (not easy to catch from the command-line BTW).  Urrrgh.  Resetting the time to the correct month on the server solved the problem.

Yay.