Hey AFR,
Really sorry that I didn't answer earlier I think I overlooked this post. So what happened is your laytheme version that you tried to install is too outdated. I'm sending the latest lay theme version to anyone who has this problem. You can send an email to armin.unruh@gmail.com , then I can send it to you, if you still got this problem.
If you can't activate lay theme as often as you want, you can send me a mail and I will reset your key!
Have a good day!