rdp cannot consistently connect to a windows server 2008 R2

Up until about 2 weeks ago, I was able to login to our Windows Server 2008 R2 every time using RDP. But now only rarely am I able to login now.

This is on a remote network with a fixed IP address. I can VNC into a macintosh on the same network and then using MS Mac RDP client, get to the same server consistently.

I checked, and nothing was installed on the server via Windows Update.

Any suggestions?

Thanks

Craig