Occasional black screens on playback MF3

[King Cole]

I usually create DVD discs with Movie Factory 3 by importing WMV files created by Photo Story 3. They usually work fine but every now and then some of my photos don't appear properly. I assign transitions, movement and durations in Photo Story 3 and the WMV files playback fine. After converting to DVD in MF3, most of them are OK, but then one that I have set to display for about 5 seconds may just appear for about one second, then a black screen appears for about four more seconds. Then it continues fine for many additional pictures and occurs again. Sometimes the black screen starts with a solid purple horizontal bar slowly sliding down the black screen. I have experimented around by changing transitions, motions and durations, but can't find any specific pattern to the random occurrence. Any ideas?