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.
There may be a prompt, but there's no mandate to update. If your version is working well stick with it; it doesn't expire and no additional fee is required. Newer releases can always be test driven, licensed or not. Just retain your old installer. If you don't have it, download from the archive here.
If there's still a problem, get in touch with the company via the appropriate link here.