I used the registration number given to me and I receive the message “Invalid License Number” Not sure what the problem is…Any suggestions?
Are you still having this problem?
The registration form can be found here.
I do not have to re-register when you update the program and/or the virus database… What is happening in your system? What avast is asking for? 
Try to register again. You must provide a valid email address and, in this email, you will have the registration key for avast!