BE SURE that you have saved the project. Click the chevron to the right of the SAVE button on the toolbar. Save Project AS, and give it a unique # or name, so as to not overwrite earlier saves.
That done, go to OPTIONS | DISK tab and Clear Unused Cache Files.
If no joy, reinstall Videopad. If those measures don't fix the issue, please share the project so others can see it and suggest or make the fix. It's easy, quick and can be private.
Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
Don't upload the exported version, just the PORTABLE project folder. If it contains sensitive material link it in a personal message (PM). Click the envelope above. It won't be passed on or retained. Use FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to share it.