I have just setup a guest account. Avast wants me to login as administrator to enter the Avast registration number. Avast is running on an administrator account that is already registered. What do I do?
I think that solution to your problem is right here.
http://forum.avast.com/index.php?topic=17989.0
Welcome to the forum!
In short, you shouldn’t have to register again. The Administrator’s registration is enough for all other users