The S.O. it is windows middle xp center, the version of Avast it is 4.8. home
NB. if I make the normal scanning it doesn’t happen the problem.
The error message is: “he is verificatoun error in Virus scanner. The applcazione will be closed.”
Grazie
Hi…
While I don’t know why this has happened specifically, you can try performing a repair installation and then try manually updating avast. Just go to the Control Panel, click on “Add/Remove Programs,” and then avast. When the menu options appear on the left (in the window that appears after clicking on avast,) scroll down to the, I believe, last option, “Repair.”
If the problem isn’t solved after performing the repair, you can try uninstalling avast with this tool…
http://www.avast.com/eng/avast-uninstall-utility.html
Then download and reinstall avast from scratch…
http://www.avast.com/eng/download-avast-home.html
If you didn’t save your registration key (e-mail,) you can apply for a new one here…
http://www.avast.com/eng/home-registration.php
Hope this helps. 
Best Regards…
We will need more information to be able to help you:
- What avast! version and VPS file (virus database) number?
- Do you use a firewall? Which one?
- Do you have any other antivirus installed in your system? Did you have in the past?
- Any other security programs that could interfere?