I was attempting to delete an executable files that used to launched at the end of installation. Advanced Installer warned me that this a "Required Item" and Search button on the dialogue found the reference correctly.
I proceeded to remove the reference (set a different executable to launched at the end of installation) and attempted to delete the executable again. This failed again with the same "Required Item" warning although Search found nothing this time around.
I restarted Advanced Installer and tried again but still no luck -- it kept insisting that executable is still referred by other items although it could not find those items. Looking through AIP file I discovered that executable had a couple of "companion" files but Search was not finding those.