Shadows have jaggies using rateriser

[James]

Hi all
Im using mental ray area lights. When I dont have the fast rasteriser on the lights are fine. When i do the shadows have jaggies/aliased.
Any suggestions as to how i would fix this. Dont really want
to use shadow maps(or do I have to)

[Dodgeas3d]

Maybe dont use fast rasterizer? if so increase samples per pixel...