Trying different proxy settings are unlikely to resolve this and more likely to cause issues as and when it is resolved. The best setting is Direct Connection (no proxy), image.
Try a repair of avast:
XP - Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow.
Vista, win7 - Control Panel, Programs & Features, uninstall a program, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow.
I would say you can try uninstalling and reinstalling. But i would wait to see what the others on the forum say
Edited: Have you tried to reset avast to default settings? You can do this by open avast> click settings> click Troubleshooting > The reset avast to default settings would be listed as Restore factory defaults
Try the Manual update of VPS - avast! Virus Definitions Update - Manual Download VPS Update (virus definitions, vpsupd.exe, approx 31MB). - Save the file to your hard disk, locate where you saved it and double click it and that should carry out the virus definitions update.
Note: Ignore the file name in the images of the page that is displayed after clicking the download link, they are for the main program, not for vpsupd.exe which will be downloaded.
If that doesn’t resolve it then a reinstall is the next option, uninstall, reboot install.
It says it updated the definitions and that they are now up to date, however, in the summary page of AVAST it STILL says: Virus definitions version 120204-1 ?!?
;D SUPER EASY FIX: I had this error message, too, on July 16, 2013 and fixed it without re-installing or anything complicated. Here’s how: In Maintenance/Update, I simply clicked on the “Update Program” button. THAT DID IT! I had Program Version: 8.0.1489.0 when I clicked. The result: the PV was already up to date, BUT it updated the Engine and Virus defintions (I went from Version 130715-0 to Version 130716-0). Hooray!