JS runtime error in vbulletin_facebook.js in IE9 only

[Exeter]

I get the following error when loading one of my form pages in IE9. Firefox and Chrome work fine. Has anyone see this before?

SCRIPT5007: Unable to set value of the property 'setActiveNode': object is null or undefined
vbulletin_facebook.js?v=421, line 11 character 1088

Since this error comes from a minified file, it is a bit hard to debug. Any help is appreciated.
The bug does not appear to have any impact, but it's hard to tell.

Thanks


Repro (IE9)
http://www.hingmy.com/forum.php

[Exeter]

This may be the cause, but I have not had a chance to test the fix properly.

https://gist.github.com/oscherler/3193052