Viewer won't advance to next image

Hello. I'm using Directory Opus 9.0.0.7. I have the DOpus Viewer set up as my default image viewer. All of the sudden, the ability to advance to the next image in the folder (with a left-mouse click or using the keyboard) is shaded out. I have already tried a full uninstall/reinstall, including deletion of my settings. Still, all options to advance to the next image in a folder are shaded. Left-click does nothing. Spacebar does nothing. Backspace does nothing.

I thought it might have been Photoshop CS3 that's causing this problem, as I recently let it update itself. But my viewer STILL won't advance even after I've uninstalled Photoshop.

Anyone have any ideas? I'm at the end of my rope here.

Did you happen to uncheck the option highlighted in red below?