Notification Center errors filling up /var/log/system.log Once per second I'm getting the following errors in my system.log:

Aug 28 01:15:00 Air com.apple.launchd.peruser.501[122] (com.apple.notificationcenterui.agent[52635]): Exited with code: 1
Aug 28 01:15:00 Air com.apple.launchd.peruser.501[122] (com.apple.notificationcenterui.agent): Throttling respawn: Will start in 1 seconds
Aug 28 01:15:01 Air.local NotificationCenter[52636]: Unable to load nib file: MainMenu, exiting


Is this likely affecting system performance, and what can I do about it?

Note that the "Air" in the log is my very creative name for the MacBook Air computer I use. Also, Notification Center is delivering notifications as expected through all this; I don't know why it's attempting to respawn because as far as I can tell, the process isn't dead.

The output of ps -x |grep otific
is

 341 ??         0:22.61 /System/Library/CoreServices/Notification Center.app/Contents/MacOS/NotificationCenter -psn_0_430185


Notifications appear as expected.

The file /System/Library/CoreServices/Notification Center.app/Contents/Resources/en.lproj/MainMenu.nib has the following ls -l entry:

-rw-r--r--  1 root  wheel   1787 Jul 25  2012 MainMenu.nib
This might be nothing but twice you referred to the file as 

"/System/Library/CoreServices/Notification Center.app" 

(note the space)

but I find the app at

"/System/Library/CoreServices/NotificationCenter.app"

on my Mountain Lion systems.

Does the path in /System/Library/LaunchAgents/com.apple.notificationcenterui.plist have the space?

If your system does have a space in that path, it could be causing problems. 

I would log out and then either login via ssh or &gt;console at the login window, remove the space:

sudo mv -vn "/System/Library/CoreServices/Notification Center.app" "/System/Library/CoreServices/NotificationCenter.app" 


and then reboot

sudo shutdown -r now