There are two Error



  var ATemplate = g_(go.Group, "Auto", {
            resizable: true,
            resizeObjectName: "SHAPE",
            rotatable: true,
            locationSpot: go.Spot.Center,
            locationObjectName: "SHAPE",
            selectionObjectName: "SHAPE",
            background: "transparent",
            mouseDragEnter: function(e, grp, prev) {
                highlightGroup(e, grp, true);
            mouseDragLeave: function(e, grp, next) {
                highlightGroup(e, grp, false);
            computesBoundsAfterDrag: true,
            mouseDrop: finishDrop,
            handlesDragDropForMembers: true,
            ungroupable: true
        }, new go.Binding("angle","angle").makeTwoWay(), new go.Binding("location","loc",go.Point.parse).makeTwoWay(go.Point.stringify), new go.Binding("background","isHighlighted",function(h) {
            return h ? "rgba(255,0,0,0.1)" : "transparent";
        ).ofObject(), g_(go.Panel, "Spot", g_(go.Shape, "Rectangle", {
            name: "SHAPE",
            fill: "rgba(255,255,255,0)",
            strokeWidth: 1,
            stroke: "rgba(0,0,0,1)",
            width: 150,
            height: 50
        }), g_(go.TextBlock, {
            editable: true,
            _isNodeLabel: true,
            isMultiline: true,
            alignment: new go.Spot(0,0,0,0),//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            cursor: "pointer"
   new go.Binding("alignment").makeTwoWay(),
   new go.Binding("font","font"),
   new go.Binding("stroke","color"),
   new go.Binding("text","text").makeTwoWay())));
 function setMode(mode, itemType) {
            myDiagram.commitTransaction("mode changed");

 var inspector = new Inspector('myInspectorDiv',myDiagram,
            properties: {
                "angle": {
                    show: Inspector.showIfNode,
                    type: 'number',
                    defaultValue: 0
                "alignment": {
                    show: Inspector.showIfNode,
                    type: 'spot'//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        function save() {
            document.getElementById("mySavedModel").value = myDiagram.model.toJson();
            myDiagram.isModified = false;
        function load() {
            myDiagram.model = go.Model.fromJson(document.getElementById("mySavedModel").value);

We generally can’t debug your code for you. You are setting some invalid Spots somewhere, and also replacing a Model during a transaction. You’ll need to determine which parts of your code are doing this; they don’t seem to be in the code you posted.