A few of our users receive the following error when attempting to establish a remote desktop session. "Your computer can't connect to the remote computer because a security package error occurred in the transport layer." For most users, connections are not a problem. The environment is as follows:
Remote Desktop Session Host - Windows Server 2008 R2
Remote Desktop Gateway - Windows Server 2012 R2 (SSL certificate has been installed and chain verified)
Client computer that cannot connect - supports RDP 8.1.
The users that cannot connect are behind a firewall at a customer facility. The do not have trouble connecting to normal secured web sites through port 443. I'm having trouble trying to determine if I have not configured something correctly on the gateway or if the customer has blocked traffic in some way that does not allow RDP. Since the transport should be HTTP (instead of RPC over HTTP), I don't think this should be a problem.
Any help in pointing me in the right direction would be appreciated.