Notification Center UI Agent error message every second

Hi - I noticed my machine was acting sluggishly, constantly accessing the disk.

I checked the Console and get this, every second:

....

11/6/12 7:54:43.633 AM NotificationCenter[15411]: Unable to load nib file: MainMenu, exiting

11/6/12 7:54:43.635 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent[15411]) Exited with code: 1

11/6/12 7:54:43.635 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent) Throttling respawn: Will start in 1 seconds

11/6/12 7:54:44.669 AM NotificationCenter[15412]: Unable to load nib file: MainMenu, exiting

11/6/12 7:54:44.670 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent[15412]) Exited with code: 1

11/6/12 7:54:44.670 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent) Throttling respawn: Will start in 1 seconds

11/6/12 7:54:45.705 AM NotificationCenter[15413]: Unable to load nib file: MainMenu, exiting

11/6/12 7:54:45.707 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent[15413]) Exited with code: 1

11/6/12 7:54:45.707 AM com.apple.launchd.peruser.501[332]: (com.apple.notificationcenterui.agent) Throttling respawn: Will start in 1 seconds

etc....

Anybody have any idea how I can stop this? It's got my hard disk constantly running.

Thanks...chico