Arcgis Engine The supplied command does not exist in command pool？

private IGeometry GetMergeGeometry()

        {

            IFeatureLayer pFeatureLayer = mainMapControl1.get_Layer(1) as IFeatureLayer;

            IGeometryBag pGeometryBag = new GeometryBag() as IGeometryBag;

            pGeometryBag.SpatialReference = GetSpatialReference();

            IGeometryCollection pGeometryCollection = pGeometryBag as IGeometryCollection;



            // 属性过滤

            IQueryFilter pQueryFilter = new QueryFilter();

            pQueryFilter.AddField("Shape");



            // 要素游标

            IFeatureCursor pFeatureCursor = pFeatureLayer.FeatureClass.Search(pQueryFilter, true);

            IFeature pFeature = pFeatureCursor.NextFeature();

            if (pFeature == null)

            {

                return null;

            }



            // 遍历游标

            object missing = Type.Missing;

            while (pFeature != null)

            {

                pGeometryCollection.AddGeometry(pFeature.ShapeCopy, ref missing, ref missing);

                pFeature = pFeatureCursor.NextFeature();

            }

            Marshal.ReleaseComObject(pFeatureCursor);



            // 合并要素

            ITopologicalOperator2 pTopologicalOperator = null;

            if (pFeatureLayer.FeatureClass.ShapeType == esriGeometryType.esriGeometryPoint)

            {

                pTopologicalOperator = new Multipoint() as ITopologicalOperator2;

                pTopologicalOperator.ConstructUnion(pGeometryCollection as IEnumGeometry);

            }

            else if (pFeatureLayer.FeatureClass.ShapeType == esriGeometryType.esriGeometryPolyline)

            {

                pTopologicalOperator = new Polyline() as ITopologicalOperator2;

                pTopologicalOperator.ConstructUnion(pGeometryCollection as IEnumGeometry);

            }

            else

            {

                pTopologicalOperator = new Polygon() as ITopologicalOperator2;

                //问题显示：使用的工具并未在工具池中找到。

                pTopologicalOperator.ConstructUnion(pGeometryCollection as IEnumGeometry);

            }

            return pTopologicalOperator as IGeometry;

        }

1、为了解决 TopologicalOperator.ConstructUnion(pGeometryCollection as IEnumGeometry);“未指定的错误(Exception from hresult：0x80004005(E_FAIL))”的问题，用管理员身份打开VS，问题变为The supplied command does not exist in command pool。