Turning off the "Use external binary morph targets" option, only stops Poser from saving PMD files, it will still read them when they're referenced by other files.

The only solution in this case is to delete the PMD file associated with the PZ3 that won't load.
You should then be able to load the scene, but all morphs will have disappeared.
The dial and material settings can be saved so that you can apply them to a fresh copy of any figure(s) (i.e. delete and reload any figures affected).