"Computer Locked" dialog does not appear

"Computer Locked" dialog does not appear

When I lock my computer, instead of seeing the "Computer Locked" dialog, I only see the "Unlock Computer" dialog with my user name populated and my password box has focus. I am not prompted to Ctrl+Alt+Del to first get to the "Unlock Computer" dialog. This concerns, as nearly all of my other Windows XP machines do display the "Computer Locked" dialog and force a Ctrl+Alt+Del sequence to get to the "Unlock Computer" dialog.