I encountered this error one day when trying to login to a terminal server and got nothing but a black screen with a cursor. Rebooting the server would fix the problem for a short while. When investigating the event logs I found the following errors:
Event ID 56: The Terminal Server security layer detected an error in the protocol stream and has disconnected the client. Client IP: xxx.xxx.xxx.xxx.
Event ID 50: The RDP protocol component X.224 detected an error in the protocol stream and has disconnected the client.
Disabling TCP Offload on the server fixed the issue:
  1. Open an administrative command prompt and run the following commands:
    netsh int tcp set global chimney=disabled
    netsh int tcp set global rss=disabled
  2. Next, open regedit and navigate to HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\EnableTCPA and set the value to 0. If the key does not exist, right-click on Parameters, select new DWORD Value, and enter EnableTCPA in the text box.