Do you mean the option doesn't appear on the context menu at all, or that it doesn't work when you select it?
If it doesn't appear, does it appear when you hold shift and right-click? If so then you've turned on Preferences - Miscellaneous - Windows Integration: Hide Windows items on file context menus (shift overrides). If you want to hide most items and don't want to hold shift to see the KAV items then you can force the KAV items to appear using the Filetype CONTEXTFORCE... command, as shown in Tip: Organise and Speed-Up Context Menus.