If creating and opening slideshow without including any image or other files, just get a plain white screen...
XnViewMP 0.91 beta 4 on Windows 7
To recreate:
Create > Slideshow > OK (without adding any files or folders). Set to full screen output.
Result: Plain white screen.
Expected: message 'No images in slide show' (or similar). Or OK button to be inactive when nothing in slide show.
Jeremy