Boolean Subtraction Issue

[dlampley.41310]

I'm having a little trouble subtracting an area out of a concrete thing that I'm designing. I have (2) mass elements that definately intersect each other, and I simply want to subtract one from the other. But for whatever reason, it just isn't working.
I've attached the model that I'm working on so you can better see what's going on. I'm using 2008 Architecture. In the model, their are 3 separate Mass Elements:
Element A - a large rectangular base
Element B - Concrete walls on top of the base
Element C - a large cube at the top that is supposed to only serve the purpose of creating a void in Element B

So, Element C is supposed to go away after doing the subtraction from Element B. Makse sense?

[dzatto]

I think it has to do with converting it to a mass element before finishing all of your subtractions. I left them as 3d solids, did all the subtractions, then converted it to a mass element as the last step and it worked fine.

I couldn't get your original drawing to subtract either. I even tried on ADT2007 also.

[fhoffnar]

The solid has some weird issue on the top left. I'd remake it I think.