Following up on Nat's observations, are you dealing with VOB files from a DVD that were then converted to mp4? How was that done?
What version of Videopad is being used? Test the latest. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
If problems persist, please upload the mp4 to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. Using Google Drive, if necessary change "restricted" to "anyone with link can view."
Be sure that the file size doesn't exceed your server allocation.