Access Violation using XMMatrix and std::vector

I'm currently having a problem in my project where I'm trying to get a Dx11 running.

My error is: Unhandled exception at 0x00FC266D in 3DTestProject.exe: 0xC0000005: Access violation reading location 0x00000000.

The Crash Occurs in my Model.cpp IN Model::Render() at this line:

cb.mWorld = DirectX::XMMatrixTranspose(aOrientation);

Because of the implementation I have to send it as a const reference in Render()

const DirectX::XMMATRIX& aOrientation

Called from Instance

m_pModel->Update();

My header for Instance looks like this:

class Instance 
{
public:
  Instance();
  Instance(Model* aModel);
  ~Instance();

  void Update();
  void Render(Camera* aCamera);

private:

  DirectX::XMMATRIX m_Orientation;
};

My guess is it is because I store my instances in Scene.h as a std::vector and I don't know how to solve it.

std::vector<Instance> m_vecInstances;