That isn't a texture.

I assume you're using a two-sided square prop for your floor?

If so, replace it with the single-sided square or ground plane. Poser 5 doesn't like double-sided geometry, and this sort of mosaic artifacting will usually occur with such meshes.

Or, if you must use the double-sided square, apply a Simple_Color node to the material's Displacement channel, and set the displacement strength to 0.01; that will "separate" the sides sufficiently to avoid the render glitch.