Super small javascript bug in internet explorer.

I have this page: [login to view URL] This page is crashing the browser, page loads slow, page unresponsive etc at first. Then errors when load modal, can't load subsequent modals etc when i checked in IE8 The error is listed as but IE fails to then load any more JS on the page so there might be more issues. 'offsetHeight' ist Null oder kein Objekt [login to view URL], Zeile 9 Zeichen 3235 Javascript crashing in IE8 (could also be errors in ie7 too. This is a simple problem, i am looking for someone that can do this fix this very moment. If you can do it now and i can see you have experience in javascript i will award it to you and give you logins etc.