Slides missing in Menu

Thanks Michael for the quick reply. I tried resetting the menu and that did not correct the problem. When I preview only the slide, the title shows in the menu like all other slides. But when I preview the scene, only a few slide titles show up. All of the slides play in sequence with the next button (OK). The slide titles are highlighted when they are shown on the screen. When the user advances to "some" of the slides with the next button, the slide appears but the highlight goes away until you reach a slide with a title displayed in the menu. The user can move from slide to slide by clicking on the title of a slide (OK). Very strange - appears that something got corrupted.