If a server has both Lotus Notes (client), and Lotus Domino (server) installed, the plug-in may not be installed in the correct directory.

Make sure that the notes.ini file belonging to Domino, has the correct reference to the pluginfile (nvcd_oa.dll) as stated in the manual. Then copy the nvcd_oa.dll file from the Notes-folder to the Domino-folder and restart Lotus Domino.