I was having the same issue: created one MP4 successfully, and now it will go through 99% of the creation process, and "stalls". I would see the file in the destination directory, but when you double-click on it, it won't play because the file is still "open". After 3-4 minutes of normal video production activity, I let it sit for 2 hours - nothing happens. When you cancel, the created file is deleted.
Details: PowerDirector 10 on Windows 7.
Solution: I installed the latest update, and that seemed to have fixed it. I have generated an MP4, made some changes, and then successfully generated another... and another. Side benefit of updating: video production seems significantly faster.
Good luck!
RayH