7.1 Issue

I purchased this program a few years back. I used it for quite sometime, but then ended up buying an actual surround sound system for my PC, so I haven't used the software in a few years. I install it today, decided to see what may be new, or that I could use. When I log in, I get this prompt for a serial number. I don't ever remember using a serial number, but it may be possible. I just figured since I had purchased it online, I should still have it. Have the terms of the software changed? Do you have to purchase it on a yearly basis? Any help would be appreciated. Thanks