Registration

I’m running Windows 7, 64 bit, and Avast free is refusing battery. I have Avast on my other computer, runningXP Pro 32 bit, and there was no difficulty at all with the registration for that machine. I’ve tried changing the compatability settings on this won, but it still won’ register; any ideas?

https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=612