Mike is right (again). The surface is contaninated with something not compatible w/ the paint. Just go down to the auto body supply house and get some wax and grease remover (Dupont name is Prep-Sol) and always use that first. I have never had a compatibility problem after using this stuff. Also, the grey primer in tha spray cans is not fuel proof and can bubble if fuel gets to it. It also does not stick all that well directly to fiberglass. You really need an epoxy primer that etches into the part and will hold. PPG or Dupont or generic stuff all works. I tried rattle can grey primer years ago and it would always crack and bubble up after a while. It will stick fine if your part is primed in the mold because the glass already has an epoxy primer on top of it.