Crash

LPDIRECT3DVERTEXBUFFER8 g_square;

struct my_vertex{
  FLOAT x, y, z, rhw; // The transformed position for the vertex.
  DWORD color;        // The vertex color.
};


my_vertex g_square_vertices[] ={
 { 250.0f,  200.0f, 0.5f, 1.0f, 0x00000000 },
 { 250.0f,  50.0f,  0.5f, 1.0f, 0x00000000 },
 { 400.0f,  200.0f, 0.5f, 1.0f, 0x00000000 },
 { 400.0f,  50.0f,  0.5f, 1.0f, 0x00000000 }
};
 

DrawBox(float Xpos, float Ypos, float width, float height, DWORD Color)
{

	unsigned char *Temp_Vertexbuff;

	//top left of box
	g_square_vertices[0].color = Color;
	g_square_vertices[0].x = Xpos;
	g_square_vertices[0].y = Ypos;
	g_square_vertices[0].z = 20.0f;
	g_square_vertices[0].rhw = 1.0f;

	//bottom left of box
	g_square_vertices[1].color = Color;
	g_square_vertices[1].x = Xpos;
	g_square_vertices[1].y = Ypos + height;
	g_square_vertices[1].z = 20.0f;
	g_square_vertices[1].rhw = 1.0f;

	//top right of box
	g_square_vertices[2].color = Color;
	g_square_vertices[2].x = Xpos + width;
	g_square_vertices[2].y = Ypos;
	g_square_vertices[2].z = 20.0f;
	g_square_vertices[2].rhw = 1.0f;

	//bottom right of box
	g_square_vertices[3].color = Color;
	g_square_vertices[3].x = Xpos + width;
	g_square_vertices[3].y = Ypos + height;
	g_square_vertices[3].z = 20.0f;
	g_square_vertices[3].rhw = 1.0f;

	g_square->Lock(0, 0, &Temp_Vertexbuff, 0);

	memcpy(Temp_Vertexbuff, g_square_vertices, sizeof(g_square_vertices));

	g_square->Unlock();

	pDirect3DDevice->BeingScene();
	pDirect3DDevice->SetVertexShader(D3D8T_CUSTOMVERTEX);

	pDirect3DDevice->SetStreamSource(0, g_square, sizeof(my_vertex));

	pDirect3DDevice->DrawPrimitive(D3DPT_TRIANGLESTRIP, 0, 2);

	pDirect3DDevice->EndScene();

}