A Lotus Notes® 6.x client attempts to replicate either by using the menu option File, Replication, Replicate, or by clicking the Replication bookmark. However, the menu option yields the error "Unable to Invoke Program", and clicking the bookmark just does nothing. Restarting the Notes Client usually resolves for a short time, but the problem reoccurs.
This issue occurs when a single Notes client install is running the Multi-user Cleanup Service. This service, ntmulti.exe, should be installed only on Multi-user systems, not on single-user installations.
On Notes client Single-User installs, check the system Services under Control Panel, Administrative Tools, Services, for "Multi-user Cleanup Service". If this service is started, stop it, and change the Startup Type from Automatic to Manual.
In one case, the service ntmulti.exe was not present in the Services, and was not running as a process in Task Manager, even though the user observed the same symptoms. Re-running client setup to generate a new names.nsf, desktop6.ndk, and bookmark.nsf resolved the issue.