I had this issue as well with a Barracuda SSL VPN box. The only way I fixed it was by messing with gpedit on the local machine. Here is another link that shows where the settings are. Follow the one for gpedit: How to Enable and Secure Remote Desktop on Windows
Play around with the settings to try to keep it as secure as possible. Since my issue was with a workstation behind company firewalls, I just disabled it all.
Hope this helps,
Jeremy