CB

This code only executes on window.onresize. This is fine in other browsers, because it only triggers this exactly in that situation. However, IE appears to fire it on first page load even though window wasn't resized. The error happens because the JS that setups the HTML and has the ID it's trying to reach hasn't fired yet resulting in an error.

Further investigation shows that IE fires this when elements on page also resize. For example if "body" resizes it'll fire window.onresize.