Cant find part files

I started to open an assembly and got the popup stating that a part document could not be found. For reasons that are unimportant to this discussion, I checked the box that keeps such popups from occurring. Now when I try to open an assembly and SW can't find the referenced part documents, I get no popup. I need to enabla that popup feature again. How do I do that?    

SolidworksAssemblies