Managed DirectX Sprites

I''m having a big problemo! I''ve got a texture that contains 128 different smaller ''sprites'' in it. I''m using the Microsoft.DirectX.Direct3D.Sprite class to render these. However, if I set the ''srcRectangle'' property to one of the sprites in the middle of the texture for example (x, y, width, height) = (25, 32, 64, 64), it throws up an exception. When i render the sprite as (0, 0, 64, 64) it''s fine tho! I''m well confused - Any ideas? Synex