Questions about use MFX_RATECONTROL_QVBR in sample_encode

I use MFX_RATECONTROL_QVBR in the SDK demo of sample_encode and  have a question:

m_pmfxENC->Init(&m_mfxEncParams)error code is MFX_ERR_INVALID_VIDEO_PARAM

Do I need other initial parameters？

My initial parameters as follow:

mfxStatus CEncodingPipeline::InitMfxEncParams(sInputParams *pInParams)
{
    m_MfxEncParams.mfx->FrameInfo.PicStruct = MFX_PICSTRUCT_PROGRESSIVE;
    m_MfxEncParams.mfx->RateControlMethod = MFX_RATECONTROL_QVBR;
    m_MfxEncParams.mfx->TargetKbps = 1000;
    m_MfxEncParams.mfx->CodecId = MFX_CODEC_AVC;
    m_MfxEncParams.mfx->FrameInfo.FrameRateExtN = 30;
    m_MfxEncParams.mfx->FrameInfo.FrameRateExtD = 1;
    m_MfxEncParams.mfx->EncodedOrder  = 0;
    m_MfxEncParams.IOPattern = MFX_IOPATTERN_IN_SYSTEM_MEMORY;
    m_MfxEncParams.mfx->FrameInfo.FourCC = MFX_FOURCC_NV12;
    m_MfxEncParams.mfx->FrameInfo.ChromaFormat= MFX_CHROMAFORMAT_YUV420;
    m_MfxEncParams.mfx->FrameInfo.Width  = 1280;
    m_MfxEncParams.mfx->FrameInfo.Height = 720;
    m_MfxEncParams.mfx->FrameInfo.CropX = 0;
    m_MfxEncParams.mfx->FrameInfo.CropY = 0;
    m_MfxEncParams.mfx->FrameInfo.CropW = 1280;
    m_MfxEncParams.mfx->FrameInfo.CropH = 720;

    if( m_MfxEncParams.mfx->RateControlMethod == MFX_RATECONTROL_QVBR )
    {
        MSDK_ZERO_MEMORY(m_CodingOption3);
        m_CodingOption3.Header.BufferId = MFX_EXTBUFF_CODING_OPTION3;
        m_CodingOption3.Header.BufferSz = sizeof(m_CodingOption3);
        m_CodingOption3.QVBRQuality = 30;
        m_EncExtParams.push_back((mfxExtBuffer *)&m_CodingOption3);
    }
    if (!m_EncExtParams.empty())
    {
        m_MfxEncParams.ExtParam = &m_EncExtParams[0];
        m_MfxEncParams.NumExtParam = (mfxU16)m_EncExtParams.size();
    }
    m_MfxEncParams.AsyncDepth = pInParams->nAsyncDepth;
    return MFX_ERR_NONE;
}