The problem you are running into is that the items are not properly indexed in the data folder. What version of DS are you trying to open them in? What version were they saved in? 

To recover those .daz files, in general, in a version they were saved in or later, but before 4.5 open each item that is in the .daz. This should allow DS to now find the things in the .DAZ scene file you previously saved, which should allow DS 4.8 to open them and save them as a DUF. 

Most annoying, and one of the major reasons the .daz format was dropped.