Since last nights Windows update I get an authentication error when trying to RDP to some of my support sites, but not all.
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Remote Desktop Connection

An authentication error has occurred.
The function requested is not supported

Remote computer nn.nn.nn.nn
This could be due to CredSSP encryption oracle remediation
For more information, see https://go.microsoft.com/fwlink/?linkid=866660 

Any ideas.

Microsoft has been steadily increasing security on CredSSP (which is used with Network Level Authentication) for the last few months in response to a vulnerability. The May update changed the default operating mode to the higher level of enforcement. RD Tabs offloads CredSSP to Windows, so there's nothing to patch within RD Tabs itself with regard to this issue. As for your issue, have you applied any CredSSP GPOs in your domain? Or are you possibly trying to connect from an unpatched system to a patched system or vice versa? How does the built-in RDP client perform? Does it give a similar error or does it work?

The article you linked describes steps needed to change the security level if you have systems that are unpatched.

In my test lab and in my day job I have a mix of patched and unpatched systems, but we haven't changed any of the default policies and I have not seen this issue come up yet.