As of Microsoft's security patch in May 2018, RDP from patched clients to unpatched hosts gives a 'function request not supported' error. In the event that one can't (for some reason) patch the host, one workaround is to change group policy on the local computer:
In gpedit.msc:
Computer configuration -> Administrative Templates -> System -> Credential Delegation -> Encryption Oracle Remediation.
Choose 'Enable' and change protection level to 'Vulnerable' and apply (restart usually not needed).
Another option is this workaround, which I haven't tested:
http://blog.fmsinc.com/remote-desktop-authentication-error-function-requested-is-not-supported-credssp/
