A poster above (I think eKurtz?) mentioned about not priming Reaper Bones without using their special primer. I paint a lot of these guys and you definately can use the primers I suggested so long as you properly wash the model first in warm soapy water. Scrub them, then rinse thoroughly in warm water again. Then they will prime fine. They have a sort of grease on them left over from the injection method and it's just that you need to get rid of. Some are worse than others for some reason!
Also, I now wash any sort of similar plastic before priming, especially the type of cheaper plastic used for boardgame miniatures...