I tried this from another post and still no luck. I am running Vista Prem 64 bit.
download the offline avast installer from here : http://www.avast.com/eng/download-avast-home.html , please use the full installer. do not download the online installer and also from cnet (download from avast site itself). select the required language.
It is the free program and the key is what I recieved in the email.
I get no error message. I says the key has been accepted but when I try to do a boot scan it is greyed out. When I try to see the license key it is blank.