Drag out of the graph's area, error happens

if the user ‘drag’ at a blank place and move out of the graph’s area then an error happens.
This is the error’s description:

SCRIPT5007: Unable to get property ‘offsetParent’ of undefined or null reference
GoWeb.js, line 152 character 3

function _getMouse(e, ele) {
var element = ele, offsetX = 0, offsetY = 0, mx, my;

if (element.offsetParent) { — error happens here
do {
offsetX += element.offsetLeft;
offsetY += element.offsetTop;
} while ((element = element.offsetParent));

if (e.pageX === undefined) { // Internet Explorer
var pageX = e.clientX + document.documentElement.scrollLeft;
var pageY = e.clientY + document.documentElement.scrollTop;
else { // Firefox, Opera, Google Chrome and Safari
var pageX = e.pageX;
var pageY = e.pageY;

var result = {
x: pageX - offsetX,
y: pageY - offsetY
return result;

Can you reproduce with http://godotnetweb.com/FlowCharter/WebForm1.aspx ?

What version of what browser? and what version of GoWeb?

Under Compatibility view mode: http://godotnetweb.com/FlowCharter/WebForm1.aspx can’t reproduce.
But under Standards mode http://godotnetweb.com/FlowCharter/WebForm1.aspx display blank.

My GoWeb version:Northwoods.GoWeb.DLL, v4.0.30319
Browser version:IE8\9\10

I can’t reproduce a blank display.

I’d recommend you move to GoWeb 5.0.