I’m running Avast Free v 5.0.418 on Windows 7 Ultimate 64-bit. Until today, I was able to right-click on a file, set of files or folder and then select the Avast “scan…” item from the context menu. Now the context menu entry is missing - the icon is gone, the text is gone. I tried editing the avast5.ini file to add “ShellExtensionIcon=1”, rebooted, but it’s still missing.
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?