Notification Center errors filling up /var/log/system.log
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