newtonBody := CreateNewtonBody(nWorld, Collision, @vPosition_.x);
What's behind vPosition_? If it's only a single vector containint the object's position that could be the problem, cause you need to pass a full matrix as the last parameter. And if it doesn't work when passing a matrix make sure the matrix' alignment is same as the alignment newton uses, dunno if Irrlicht uses a different alignment or something. It has to be a correct 4x4 matrix with valid values or troubles will arise.

Other than that I can't see what's wrong cause you're using a lot of Irrlicht-related stuff and datatypes. Maybe offload everything to a separate app without Irrlicht and try it there again. Or get the basic SDL-demo from my page and take a look at it's source code.