Since I installed the home edition on my PC with Windows 98 second version, I can’t scan or defrag hard disk C any more. I have to reinstall Avast every time and download it again and asked for a new registercode. This costs a lot of time and drives me crazy. Who knows a solution?
Win98 is notorious for having problems with defrag it needs virtually every program stopped (using CTRL+Alt+Del and stopping them). There are also better and quicker derfag options out there.
The easier option is to boot into safe mode (avast doesn’t run automatically in safe mode you have to manually start it), that will also stop other non essential programs that usually start on boot.