Weird stripes on a Poser background?

eponica

Hi again ^_^

I seem to be asking a lot of questions lately. Anyway, I have here an older scenery prop made for Poser 7. The prop loads fine in DAZ but the background image has vertical stripes on it under certain lighting, like the Uberenvironment 2 lights. If I change the Environment Mode to Ambient only, they disappear. If I'm in an Occlusion with Shadows mode, the stripes vanish when I zero the Occlusion slider. I tried putting the background image on the Millennium Environment plane instead of the included plane and it still happens. But why? O_o;