If your antivirus client stops working after upgrading Windows

If you upgrade your Windows operating system from a previous version without first removing your antivirus software, you will likely run into problems. This is especially true when upgrading with a Symantec application installed; the antivirus client will stop functioning, and you'll be unable to reinstall it or install another client. At this time, the only solution to this problem is a clean reinstall of Windows.

To prevent this, completely remove your antivirus client before upgrading Windows.