Normally, there is backward compatibility within a series. Yet in recent versions significant improvements have been made that change the way some features are processed. This could explain the problem. You have the project file, so you're safe.
To complete it, install the version used to create it. Usually the installer is saved in this path on the PC: "C:\Program Files (x86)\NCH Software\VideoPad"
Or get it here and install. Go to OPTIONS|DISK tab and Clear Unused Cache Files. Then load the project. If this doesn't resolve the issue, visit the forum again.