If Videopad automatically reloads the project go to OPTIONS | DISPLAY and select New Blank Project... 
Then launch it and, with nothing loaded, click the DISK tab and Clear Unused Cache Files.
Video editing is resource intensive, needing lots of RAM and a higher end processor and video adapter for large or complex projects.
Try breaking the project into more usable chunks, exporting each, then assembling the exports for the final. Use this 64-bit release.
For one-time licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee is required in order to register the newest. Retain your old install file and registration info. If there's an issue, you can always revert.