Collisions don't work with Render Tween Method

I'm trying to implement Mark's Render tween method from the castle demo into my own engine, but it's fighting me all the way.

Basically, with the render tween method in place, the collision detection doesn't work.

When I remove render tweening - and just have a clean game loop, the collision detection does work.

Any Ideas?

Regards,

Rogue Vector

you'd have to paste all your code..