Problem with Accordion and IE7/8

Problem with Accordion and IE7/8

Hello!
I'm having really big trouble with getting Accordion to work under IE7/8. I've even tried running older versions of jQuery/jQueryUI. When I'm running my website using IE, I get an error:

"Unexpected call to method or property access"

I checked lines where it occured and looks like that it's connected with appendBefore function (jQuery). I think jQuery UI uses it in order to create code needed for Accordion. Unfortunately, I have no idea what's wrong. I'm using whole <div> with sub-<div>s as accordion's headers. Maybe that's the problem?

Please, could you check this out?
login: demo
password: demo

Accordion is used in page after you log in. I'll be very thankful for any help.