.
You have 60 days unrestrected use using the demo key that is a part of the trial version before you actually need to enter a key.
Q: “Invalid license number”. Why? http://www.avast.com/eng/faq-registration-license.html#idt_220 Or Insert Registration Key - Video
Well some information would help.
- What Operating System are you using ? is it up to date ?
- What avast! version and VPS file (virus database) number, e.g. 0436-4 (see about avast!) ?
- What was the virus name, what was the file name, where was it found
example (C:\windows\system32\infected-file-name.xxx) ? - What actions have you taken to try and resolve the problem ?
Earlier today in the bottom right corner of screen it said critical error…I had to re-program my comp a few days ago, so the cd I was using was a bitout of date, therefore I need a new license number. It is not letting me do it. Avast icon (red) says it cannot scan anything it is out of date. I have avast residnet protection 4.5. Support willl not e-mail me back. I just need to get my license # in so i can take care of virus. 
It will not let me enter the 9th number or letter. It says I need to update but the license key box won’t work properly.
Better will be uninstalling this version and download the last 4.7 one, installing the new one.
You can register again and receive a new key: https://secure.avast.com/scripts/register.php?lang=ENG
See the tutorial: http://www.avast.com/files/tutorials/insert_key.htm
Please take a look here: http://www.avast.com/eng/i_was_successfully_r.html