WorkSpaceFactory.OpenFromFile打开失败是为什么 异常

用WorkSpaceFactory.OpenFromFile打开失败是为什么，编译显示：异常来自 HRESULT:0x80040258
我检查了端点句（也就是OpenFromFile处）以前，值能传进去。
求高手解答  private void button1_Click(object sender, EventArgs e)
        {
            System.Windows.Forms.OpenFileDialog openFileDialog;
            openFileDialog = new OpenFileDialog();
            openFileDialog.Title = "打开shp文件";
            openFileDialog.Filter = "shp layer(*.shp)|*.shp";
            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                string file = openFileDialog.FileName;
                string filePath, fileName;
                int index = 0;
                index = file.LastIndexOf("\\");
                filePath = file.Substring(0,index);
                fileName = file.Substring(index+1,file.Length-index-1);
                IWorkspaceFactory workspaceFactory;
                IFeatureWorkspace featureWorkspace;
                IFeatureLayer featureLayer;
                IWorkspace workSpace;
                workspaceFactory = new ShapefileWorkspaceFactoryClass();
                workSpace = workspaceFactory.OpenFromFile(file,0); 
                featureWorkspace=workSpace as IFeatureWorkspace;
                featureLayer=new FeatureLayerClass();
                featureLayer.FeatureClass=featureWorkspace.OpenFeatureClass(fileName);
                featureLayer.Name=featureLayer.FeatureClass.AliasName;
                this.axMapControl1.AddLayer(featureLayer as ILayer);
                CreatePolyline();
                this.axMapControl1.Refresh();
            }
        }