I think that Poser is somewhat fussy about how its png's are saved. I had this problem when creating thumbs in PSP, I saved them out as png's and got the strange transparency. I don't know anything about Photoshop or Illustrator but I do now have the old Fireworks MX and succeeded in saving correctly there. It seems that there are some extra settings you can use to save your png, I set mine to 'png 8' and 'no transparency'. I don't know what this means, I got through trial and error.