This error message has been coming up for literally years. It seems to happen whenever the current screen is changed somehow; it happened in XP when you locked the screen (win + L) or when you pressed CTRL + ALT + DELETE and it brought up the menu, and it's still happening with Windows 7, only it's even more frequent. Not only does it come up when you lock the screen or go on screensaver, but it also comes up when you get a UAC pop-up asking you to allow something.
Please fix it, it's long overdue.