Check to make sure that there are no firewalls in place blocking communications between the server where you are running Infrastructure Manager and the port that the ntservices probe is using.
Another customer had the UIM ports opened in their firewall (48000-48100), but they mistakenly set the first_probe_port on the robot where they had the ntservice probe installed to 4800. All communications to the probes on this robot were blocked. This was corrected by changing the first_probe_port to 48000 in the robot.cfg file and restarting the robot.