I was using v188.8.131.52 and just downloaded v184.108.40.206. The activationKey.vkf file is in the same directory as the program,
C:\Program Files\Video Thumbnails Maker
but the new version does not recognize the key, and comes up in "free" mode. How can I get it to recognize the activation key?
I found the problem. The installer put the new program on the D drive instead of on the C drive. I deleted the program on the D drive and re-installed it on the C drive, and it now works.