grass & glass render problem 3ds max 7

hi

3ds max 7 using

when i have just glass in my animation everything renders really quickly which is fine.

However when i put the grass in that i have made with the use of a scatter, and the render of the animation takes forever?????

no matter if the grass is nowhere near the glass it takes ages to render.
(talking about a small thumb of grass)

any ideas?

many thanks
mark