I think I have the answer.
When you install ActivePhone, it changes the overall ActiveHomePro application.
It removes the "ActiveHomePro" registration line, and replaces it with one for "ActivePhone." I don't know if this is a bug or not, but I'll mention it to the developers.
I figured out how to change it back.
There is a registry key. It is pretty buried down there (under one of those really long alphanumeric "CLSID" strings).
Do a search for "isActivePhone" (without the quotes), and you should find a value that is set to "1".
Make sure AHP is closed, and change it back to "0".
Restart AHP, and you should see the registration line for AHP again. You should then be able to enter your key.
Let me know how that goes.