ZBrushCentral

Boolean Operation issue?

Was wondering if someone could assist.

I am trying to do a Boolean cut operation (Using the live Boolean) with an imported STL that I converted to a Dynamesh.

Im basically trying to make a negative mold of it. So I append a standard cube, convert the cube to a dynamesh as well. When I hit the subtract the imported model that was conveted to Dynamesh does nothing. However when I append another basic shape from the toolbox and subtract it works fine?

Any guidance would be greatly appreciated. Please note I am a newbie user as well.