Review the information about ndsrep in Subscriber Channel.
Make sure you have copied the necessary files for your platform, as described in Copying ndsrep and notes.jar to the Required Locations.
(Windows only) Add C:\lotus\domino (or the appropriate Domino executable folder) to your system path, then reboot the computer.
Before trying to load ndsrep, ensure that the Identity Manager driver for Lotus Notes has been started at least once.