When trying to connect to a server or machine via Remote Desktop Connection you will get the below error which is strange as one would normally connect without any issues.
“Remote Desktop Connection
An authentication error has occurred.
The function requested is not supported
Remote computer: XXX.XXX.XXX.XXX”
After some research I found that this is due to a Windows Update patch which was released recently that is CVE-2018-0886 for RDP. So if the workstation was updated and the server was not yet.
There are two options for this.
Patch the server with the CVE-2018-0886 (Recommended)
Update the policy on the local computer (Not recommended but in case of emergency)
On the computer open Group Policy
Go to Computer Configuration > Administrative Templates > System > Credentials Delegation
Change Encryption Oracle to Remedition to Enabled
Change Protection Level to Vulnerable
Open MSTSC and you will be able to connect to the server.