I purchased the Vestal Crown, and it looks great. However, the material isn't working for hiding the wire frames. I'm aware that Poser products can be used in Daz, and I haven't had a problem before now. But the wire hiding materials won't work. Is there any work around for this?

Some Poser products work in DS - not all. Your problem may well be a type of file the mat is DS does not read all Poser files - never did. If the Wires are a separate mat zone then you can just zero the opacity/cutout in the surfaces tab.

And if they don't already have their own surface group you could use the Geometry Editor tool to give them one.