At times you will encounter the error as above when you are trying to remote desktop to the server, and therefore you may perform the below steps:-

 

Start > Run > type in the command as “mstsc -v:ServerIP:RDPport /F -admin”

 

Enter the administrator login and password as usual and once you are logged in to the server may proceed to:-

 

Start >> Administrative Tools >> Terminal Services Manager >> Select the user and log off