Give this a try:
[ul][li]fully exit Opus (via File / Exit Directory Opus)[/li]
[li]Using Explorer (or something that isn't Opus), delete C:\ProgramData\GPSoftware\Directory Opus\dopus.cert[/li]
[li]Re-launch Opus[/li][/ul]
If the 30 day stock certificate hasn't expired yet, that should put you back on that, with the ability to switch between Light and Pro until it runs out.