I was using version 7 up until last week when I saw that my virus and engine definitions had not been updated for 2 weeks prior to that! My mum using the computer more than me these days and she hadn’t noticed. So, I went to the Avast website and downloaded the VPS file for that version, but all it did was change the program version to the latest one (version 10) after the computer was restarted, so it looks like versions 9 and 10 are the only ones that will be updated from now on, which is fair enough. I knew that the program version I was using was outdated by almost three years, so I’m not overly surprised!
Yes, Avast moved on: https://blog.avast.com/2015/05/06/support-for-older-avast-windows-consumer-version-will-end/
For more on this error, read the Avast Webforum topic that I started 10/12/15 titled “Avast4.8 stopped working on Win98SE”