Did the Avast subscription expire on one of the machines?
For the machine that is working properly, you can probably just do an upgrade from the Avast GUI.
If you don't want to do the uninstall/clean install, you can try doing an
Avast Repair first to see if that resolves the problem, reboot, then try to upgrade through the GUI:
XP Users:
- Go to Control Panel > Add/Remove programs > Avast Antivirus.
-
Scroll down and choose Repair function in the pop-up window.
- Reboot.
Vista & Win7 Users:
- Control Panel
- Programs & Features
- Uninstall a Program > Select Avast Antivirus
- Click the Change/Remove button and
scroll down to Repair
- Click Next and follow.
- Reboot.
Here is how to do an
uninstall/clean install of Avast:
1. Save a copy of Avast and save it to your HDD:
Avast Free AV:
http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe2. Download the Avast Uninstall Utility
http://www.avast.com/uninstall-utility and save it to your HDD.
3. Disconnect from the Internet at this time.
4. Go into
Safe Mode (hit F8 repeatedly) and run the Avast Uninstall Tool. Uninstall ALL previous versions and products of Avast you had on this machine and reboot in between each uninstall.
6.
Reboot.
7. Install the newest version of Avast and
reboot.
8. Get Internet access and register your copy for Free online.
Free –
http://www.avast.com/registration-free-antivirus.php9. Update the Avast definitions.
Knowledge based article:
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=504#idt_0003