When you try to remove either a Custom Action or a DLL Action from your setup project, VisualSetup verifies all the occurrences of the action you are removing and shows you them. You can either continue removing the action or cancel it.

If you remove an action that is used in some event, an undefined action will be referenced in this event and setup compiler will not be able to generate your setup program. So, it is strongly recommended that you only remove unreferenced actions from your project.