这是什么错啊？

lsaturn

报这个错：Direct3D9: (ERROR) :Neither hDeviceWindow nor Focus window specified. CreateDevice Failed.The thread 0x688 has exited with code 0 (0x0)
我想是下面这句的问题吧
g_pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd,D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &g_pd3dDevice)
我有赋值给hWnd啊，是用CreateWindow创建的窗口啊！太郁闷了！