Have you selected any ports to monitor yet? There is a known bug that if you have zero ports monitored, this error will occur. Try running Port Discovery Settings -> UDT Settings -> Port Discovery. This will take you through the process of selecting the ports you want to monitor. Most people will simply select all to monitor.
After you first installed, you should have been taken through Network Sonar Wizard to add your nodes (switches and routers). After Network Sonar, you should have see the Discovery Central page with a link to the UDT Port Discovery.