Question : Problem: RDP Quit Working last week

We have a colo location with 4 servers.  All of the servers have allowed our staff to RDP to each server.  Last week, one server quit allowing RDP connections.  We get the following error message: "Your Remote Desktop session has ended, possibly for one of the following reasons: The administrator has ended the session., An error occurred while the connection was being established., A network problem occurred."  Since it is only one of the four servers with the problem, I assume it is not a network issue.  I can remote into the server using VNC, Dameware and ILo, so it appears to be tied to RDP.  Of course I don't want to use VNC, ILo or Dameware for our staff, so I need the RDP sessions to work.  Our GPO has the windows firewall off so I don't believe it to be a firewall issue.  
I read in one area that windows defender can disable the port used by RDP.  How can I enable this port again and how can I create an exemption in Windows defender that will prevent this from happening again.

Answer : Problem: RDP Quit Working last week

Gave up, called Microsoft and paid for a support ticket.  They couldn't fix it either, but about 6 days ago, it started working again.  Who knows?!?!?!?