[MSCE C#]LocateSubEntityTool工具运行时崩溃

老师 您上面的程序 为什么执行不了OnModifyComplete, 程序执行到OnElementModify就崩了

class TestModifyFaceTool : LocateSubEntityTool
    {
        public static void InstallNewInstance()
        {
            TestModifyFaceTool myTool = new TestModifyFaceTool();
            myTool.InstallTool();
        }
        protected override SubEntity.SubEntityType GetSubEntityTypeMask()
        {
            return SubEntity.SubEntityType.SubEntityType_Edge;
        }
        protected override bool OnModifyComplete(DgnButtonEvent ev)
        {
            SubEntity[] subEntityArr = new SubEntity[0];
            GetAcceptedSubEntities(ref subEntityArr);
            foreach(var curSubEntity in subEntityArr)
            {
                CurveVector cveVec;
                Convert1.SubEntityToCurveVector(out  cveVec, curSubEntity);
                if(null!=cveVec)
                {
                    DraftingElementSchema.ToElement(Session.Instance.GetActiveDgnModel(), cveVec, null).AddToModel();
                }
            }
            return base.OnModifyComplete(ev);
        }

        public override StatusInt OnElementModify(Element element)
        {

            return StatusInt.Error;
        }

        protected override void OnRestartTool()
        {
            InstallNewInstance();
        }
    }