Possible mistake is:

1. Not only register key but also user name must be entered correct too.
For example, you submit order as Alex Rest. Probably, user name in your computer is not Alex Rest and you did not edit it in the register dialog of the product. I.e. "A. Rest" or same name is not correct. Correct only Alex Rest in English language and case sensitive!

2. The user name is case sensitive.

3. You try installing other product (Alarm Master Plus instead Alarm Master, for example).