arcengine isaveas2 Failed to copy raster dataset

Question

The source code are following: when run into the last pSaveAs.SaveAs... then the computer say "failed to copy raster dataset".

The source code are following:

private void SaveRaster(IRasterDataset2 mygeoDataset,string sFormat,string filePath,string fileName )
        {
            `ISaveAs2` pSaveAs = mygeoDataset as ISaveAs2;
            if(!pSaveAs.CanSaveAs(sFormat))
            {
                MessageBox.Show("no support file type");
                return;
            }
            IWorkspaceFactory pworspaceFactory = new RasterWorkspaceFactoryClass();
            IWorkspace pWorkspace = null;
            pWorkspace = pworspaceFactory.OpenFromFile(filePath, 0);
            pSaveAs.SaveAs(fileName, pWorkspace, "GRID");
        }