OK, I have solved my problem. Solution may help OP as well.
With the help of a casual comment from the on-line chat guy, Dave, I have worked out the problem. Nothing to do with drivers, the PX engine, or other services etc. The project was corrupt. Even though it played perfectly in PhotoShow it had trouble burning to DVD or even exporting to WMV or MPEG. I re-created the project from scratch by:
1. do a save after each step
2. add photos
3. remove all music
4. arrange photos in correct order
5. set up titles, borders etc
6. put desired music in
7. then save as new project (this will reset the title so go back and retype that) then burn to DVD
8. et voila it works
9. also every time you want to re-burn or export, do a new "save as", reset the title, and then do the burn etc.
Not saying that this will fix OPs problem but it worked for mine and the symptoms were the same.