Avast! Real time shields not working?

My real time shields in Avast! Internet Security are not working and when I click “Fix Now” it does not fix. How should I solve this error?

Thank you for your time.

Are you upgrading avast or changing the antivirus?

Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove. Then choose Repair function in the popup window (Repair).
If this does not help, can you uninstall / boot / install / boot again?

What was your previous AV ?

If avast how did you install AIS, install over existing installation, entered license key into existing installation or did you do a clean install of AIS (uninstall previous version, reboot install AIS) ?