I wished that I could help Bill.
(I have Win 7 and just installed that version of IrfanView, without any problems, right into my Program Files (x86) folder.) I would guess, uninstall and check you install options, carefully?
My problems is with the Slideshow Mode and their Full Screen Options (Full Screen / Slideshow). None of them seem to be working or holding within Full Screen Mode? :(
IrfanView 4.33 on 03 April 2012, reviewed by: bill