What version? Look at the bottom-left of the window. Try 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 the VOB file names are the same, try adding incremental numbers to each - VOB1, VOB2, VOB3, etc. prior to importing them into Videopad.
Share a few files that have the issue and someone will check it out. Very easy. Upload them to a free server such as Google Drive or MSOneDrive, get a shared (public) link and post that link here.