Make sure that you have selectet an agent machine under Machine Configuration tab in Conductor. Only selected agent machines will be available for selection in Machine Assignment screen.
You may look for machines with the Discover Machine button on the Machine Configuration tab. It no machine is being displayed, then confirm whether agent services are running at the respective agent machines.
The condusctor sends out a packet to determine if a player agent is running. When traversing different subnets, hardware may prevent a packet from being accepted. Try to manually add a machine via host name, or better yet, IP.