I have been having the exact same issue and fixed it by moving openBISPushListener out of the onload event as follows:
Change
<script type="text/javascript" charset="utf-8">
function onLoad() {
openBISPushListener();
}
</script>
...
<body onload="onLoad()"> to
<script type="text/javascript" charset="utf-8">
openBISPushListener();
</script>
It seems that the onLoad event gets fired too late so that the push listener is not declared in time to catch the notification, thus causing an exception. I understand it is better practice to defer loading of javascript but unfortunetly this is the only solution I can think of at present . . .
