Disabling firewall & anti-virus did not help.
However I think I solved the issue. I enabled both SMB 1.0 and a two additional discovery functions on the Windows machine. At first that didn’t seem to help and then decided to remove the SMB 1.0 feature as I made two changes in one time. After disabling the SMB 1.0 feature all that remained was the automatic (delayed) start of two Function services. It appeared that was the trick; all of sudden the ROON client connected to my ROCK! Just to be sure I turned off the Windows machine and put it on again; ROON was still able to connect to ROCK!
Below a picture of the services I enabled; the top one is set to automatic, the second to automatice delayed.
