wimvdb, will the free version create the thumbnail?  

No but P3dO generated thumbnails are not as cute as Poser renders, far from it. The best is to save a Thumb and put it in the same directory as where the PZ3 is. P3dO will merge both thumbnails and PZ3 as it does with other Poser files. This will work with both the free and pro versions of P3dO.

Yarp - author of P3DO Organizer for Poser