Hi David, any details you could provide would really help :) Such as;

1. All Versions of blender + crowdrender you're running on both machines

2. Any error messages?, there are logs capture on both machines in the user\cr\logging folder

3. Are you running a firewall on the windows machine, if so does it allow blender to listen on any TCP ports?

4. If you know how, would be handy to check if the windows machine is running any other processes that are listening or connected to TCP ports in the range 9000-9025, if there are, or you suspect there might be, you can try moving crowdrender to a different port range by going to blender > preferences > addons > crowdrender > expand the addon and go to the 'networking' section and then select a new port number for the 'start port'. I'd recommend trying 9669 for this value.

Regarding 2, if you want to send us logs, please upload them with a support ticket at https://www.crowd-render.com/report-a-problem :)