I have found that I cannot load several of my models... nothing from Darkworld, Tempesta3d or Sabby. I haven't tried others but I suspect the same. My custom figures are fine but my vendor modes are largely absent. I have reloaded, turned Poser off and on, turned the desktop off and on still the files don't appear. I am loading the models exactly where they were before but they are not appearing. Is there a fix for this?

When you say 'load' do you mean they were already in your library but now they aren't? Did you add your previous libraries or you tried to reinstall? Also when you say 'models' do you mean figures, props, hair, or...?

I updated to Poser 12, recovered all my libraries but many figures and poses didn't make the trip. Some have the folders but no files in the Library. Also some of the materials are funky. In one Darkworld model the chest and hips come out normal but the arms and legs are black. My CMB56 Xeni the mat is great expect for the face which is black the the morph doesn't work. What might I have done (or not done) in the migration process to cause this.

I think what happened (because I also experience this) is that materials or matposes need to be reapplied when you load a figure or a matpose. As to what causes folders showing up empty, that IS wonky. You may want to reinstall Poser 12.

Do they work in Poser 11 (assuming you still have Poser 11 on your computer).

Poser 12 shouldn't affect your existing runtimes. You should be able to just attach your old Poser 11 runtimes. I am running both Poser 11 and Poser 12, and they are using the same runtimes with no problems (except for Python scripts). I have some Darkworld items, and they work fine for me in Poser 12.

I'll do a reinstall and hopefully that will resolve the issue.