If a user is on the lastest version of Windows 10 they may not be able to RDP onto an internal server and get the following error 


To fix this, the latest patch has to be installed on the server so that it is up to date with the PC that you are trying to access it from.


The current patch that fixes the issue can be downloaded from this link 


https://www.catalog.update.microsoft.com/Search.aspx?q=KB4103715



The server will then have to be rebooted to apply the update. Once done you should be able to gain access.