设置PageLayoutControl的GRID样式为何导致程序崩溃？

<P>函数如下，不知哪里出了问题：</P>
<P> private void Grid(object sender, EventArgs e)<BR>        {<BR>            IActiveView pActiveView;<BR>            IGraphicsContainer pGraphicsContainer;<BR>            IMapFrame pMapFrame;<BR>            IMap pMap;<BR>            pActiveView = axPageLayoutControl1.ActiveView as IActiveView;<BR>            pMap = pActiveView.FocusMap;<BR>            pGraphicsContainer = pActiveView as IGraphicsContainer;<BR>            pMapFrame = pGraphicsContainer.FindFrame(pMap) as IMapFrame;<BR>            IStyleSelector pStyleSelector;<BR>            pStyleSelector = new MapGridSelectorClass();<BR>            bool m_bOK;<BR>            m_bOK = pStyleSelector.DoModal(axPageLayoutControl1.hWnd);<BR>            if (!m_bOK) return;<BR>            IMapGrid pMapGrid;<BR>            pMapGrid = pStyleSelector.GetStyle(0) as IMapGrid;<BR>            IMapGrids pMapGrids;<BR>            pMapGrids = pMapFrame as IMapGrids;<BR>            <BR>            pMapGrids.ClearMapGrids();<BR>            if (pMapGrid != null)<BR>            {<BR>                <BR>                pMapGrids.AddMapGrid(pMapGrid);<BR>            }<BR>            axPageLayoutControl1.Refresh(esriViewDrawPhase.esriViewBackground, null, null);<BR>        }</P>

<P>请高手指点！！</P>