This could be due to encryption oracle remediation error
An authentication error has occurred.
The function requested is not supportedRemote computer: X.X.X.X
This could be due to CredSSP encryption oracle remediation.
For more information, see https://go.microsoft.com/fwlink/?linkid=866660
This error occurs after trying to access machine via Remote desktop connection
CAUSE : Microsoft enforcing March 2018 CVE-2018-0886 from May 2018 updates and so after May 2018 update – KB2693643 users may face this issue. 
To resolve this issue follow Solution 1 or Solution 2
SOLUTION 1 : Disable Network level authentication in Remote machine which will be available in ‘Remote’ option under ‘system properties’ .
SOLUTION 2 : Download and install your machine with update KB4093120 released on April 17,2018 available in this link( Reboot required)
SOLUTION 3 : Update your registry value in following your machine in following location with DWORD as
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\CredSSP\Parameters] "AllowEncryptionOracle"=dword:00000002