As of May 2018, I'm seeing several instances of errors connecting to terminal servers due to CredSSP errors. Microsoft released a fix that needs to be applied to both the client and the server. If one is patched, the other needs to be patched. If one is patched and the other is not, the connection will fail.
The download will vary based on the OS of the unpatched system. Here's the link
https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2018-0886
Here's what the error looks like: