I had an issue with the Windows Security Centre too. I had updated the program from within the program itself, rebooted but still had the Windows action centre pop up saying “start Avast anti virus”. Even clicking that didn’t resolve it.

Downloading the uninstaller then doing a clean reinstall has sorted the security centre not seeing Avast as having started but there is clearly an issue for some who just update through the program itself.

Windows 7 64bit.