Error using dhtmlxMenu with dhmlxGrid

The menu does not work and I get the below error when loading page with dhmlxMenu object attached to a Grid:
Error message: polygon is undefined

Here is my code:

i am constructing the Menu Object in below function:

function loadGridMenu() {
menuGrid = new dhtmlXMenuObject();
menuGrid.addNewSibling(null, “bulk”, “Bulk Action”, false);
menuGrid.addNewChild(“bulk”, 0, “own”, “Own”, false);
menuGrid.addNewChild(“bulk”, 1, “resolve”, “Resolve”, false);
menuGrid.addNewChild(“bulk”, 2, “reject”, “Reject”, false);

// Hot Keys for Menu Items
         menuGrid.setHotKey("own", "Ctrl+O");
         menuGrid.setHotKey("resolve", "Ctrl+R");
         menuGrid.setHotKey("reject", "Ctrl+J");


And i call this method as a Right Click event in a Grid as below:

         mygrid.attachEvent("onRightClick", loadGridMenu);

The first element of context menu needs having menuGrid.topId as parent id:

menuGrid.addNewSibling(menuGrid.topId,0, “bulk”, “Bulk Action”, false);

instead of

menuGrid.addNewSibling(null, “bulk”, “Bulk Action”, false);