No printing of the Lens Transparency with bitmaps

I have been having an issue with the Lens Transparency effect and bitmaps . When I apply a square lens transparency over a square bitmap and group them it looks fine on my screen but parts of the final image are always missing when I print . I have duplicated this error a number of different ways and with two different video cards . I am running XP and have 3 gigs of RAM .Any ideas what it could be ?