This is something specific to WinRT and the C++/CX extensions specifically. C++/CX does not allow ref classes to contain public fields. You need to replace your public fields with public properties.
ref class Placement sealed
{
public:
Placement(
float rotX,
float rotY,
float rotZ,
float posX,
float posY,
float posZ
);
property float rotX;
property float rotY;
property float rotZ;
property float posX;
property float posY;
property float posZ;
};
Properties have getter and setter functions generated automatically for them by the compiler.