I gave up and just re-registered, so far it's working now.
Do you mean your key is correct? 18+8
Yes that's what I meant.
Are you the Windows XP Administrator in this computer?
Yes I am the administrator.
Is there any other administrator accounts?
No, I am the only user on this computer.
Did you use the trial period or you're just registering the Home version?
I have been a registered user for over a year. I recently bought a new computer and needed to install Avast on the new computer. I tried to input my last registration key but received the error message
"The parameter is incorrect"
as stated in one of my posts above.
I viewed the suggested links...
http://www.avast.com/eng/faq-invalid-license-number.html Or Insert Registration Key - Video
and did not get any new results after. I finally gave up and just re-registered. The new key was accepted and so far the program is working ok.