At least we know it isn't a Poser issue. The problem is with the drop shadow.  Again you are seeing the effects of antialiasing between your image and your PSP background colour (blue)and the drop shadow.  You said it is fine in PS so my advice is to use PS. Or try colour filling the background in black instead of blue.

Are you making these images to give away or sell to taggers?  If so my advice is to not put in a drop shadow at all and to leave it up to the user.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi