RDP 5.x Registry Hack

RDS 2008, 2008R2, and 2012 will not allow connections from older RDP 5.x clients.

To get around this add the following registry key to the RDS Session Host

Subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM
Registry entry: Use512LenPropCert
Data type: REG_DWORD
Value: 0 or 1

This is far less secure (512bit encryption vs 2048bit), and you won't be able to take advantage of the features of later versions of the RDP protocol, but older clients will be able to connect.