I have a Win2008 server farm with RD enabled and is set to recieve connections from NLA clients only.
From windows vista and above, connnection is allowed but not with Win XP cos it's not running RDC >6.0 with CredSSP enabled.
First, upgrade your RDC version here, and enable CredSSP using the fix here. i would advice using the 'fix it for me' solution, its way easier and simpler. you would have to restart your system after that.
After restarting, when attempting to connect, it gives you the below error.
To counter this, install this hotfix and reboot.
After reboot, try it, Voila!!!!! it works!!!