[VRay]

I think Sterlind already covered about as much as could fit in a casual comment online.. The basic idea is that you draw a box around your system, then check all the inputs and outputs. If the inputs are good and the outputs are bad, you open the box and draw boxes around what's inside.

Don't be afraid to dig through heap dumps or decode assembly if you have to, although when you hit that point you're probably just going to have to swap out whatever component is misbehaving