I just had this problem with TT 2020. Turns out the logic TT uses for determining if you are using the same computer or a different computer includes examining the drives plugged into USB ports. I had a backup drive plugged into one of my USB ports when I originally installed and activated TT on my laptop. The next day, I launched TT without the USB drive plugged in, and TT prompted me for my activation code again. I tried re-launching TT several times, each time with the same result. Then, I made one and only one change: I plugged in my backup drive in the USB port. Sure enough, TT then launched without prompting me for my activation code. I believe TT should be smarter about determining whether it is being launched on the same or different computer!
