@jta
Maybe try this: register program; shut down all running processes but Explorer and Systray; DELETE EVERYTHING in Windows\Temp; use the menu button on top left of Simple user interface to select update program only; then ditto update database only; then go surf for a while and wait for next update.
This worked for me. Otherwise uninstall, use uninstall tool, clean install ra ra from avast website.
Please, moderators, WE KNEW (thanks to DaveR), 5 months ago that the CNET link was a problem... so why can't we have proper instructions on the main Avast website for win98se users? We may be a minority, but we are NOT going away!