Hello DavidOrde,
Since other computers are connecting successfully, this may mean that there is some connectivity issue to communicate correctly between the Mac computer and the RDS server.
I would recommend the next steps:
- Ensure that the Mac is connected in the same network segment as the other computers. In occasions, a machine connected via Wifi versus machines connected via Ethernet cable may work in different subnets, which traffic may or may not be routed in the same way.
- Check for network filtering: In most cases, there is a firewall or security program that is blocking the connection. Check your Mac computer for security software and add exceptions for the RDS server IP configuration and port (by default, port 3389, but could be different based on the RDS administrator choice)
- Ensure that RDP client has been updated. Try to download the latest version of the Remote Desktop client for Mac, since some previous versions would see their attempt to connect rejected as they may have security flaws.
--If the reply is helpful, please Upvote and Accept as answer--