Problem with LR4 slideshow module

[Mark F]

When I export a slideshow to video the resulting .mp4 file is totally out of order. Have no idea why or how to fix it. Woud appreciate any ideas. I'm using LR4 and OS 10.6.8.

By the way, has anyone found a good Mac slideshow plug-in for LR4?

Thanks.

[Mark F]

As a follow-up, I've identified the circumstances under which this happens - when I try to combine two separate collections into one slide show by highlighting both and clicking the export button. I've tried multiple times with the same and with different collections and the same result. I guess I will have to make one large collection and cannot use two smaller collections.