JqueryUI v1.6 Final vs IE7

JqueryUI v1.6 Final vs IE7


I am trying to update the jqueryui of Zenphoto to the 1.6 Final
release but am having troubles with our implemetation of image and
album sorting (using sortable). Everything works fine on the 1.5.3
version and with both versions on FireFox.
With 1.6 Final IE is throwing a Javascript error. It is complaining
about something not being an object on line 3301 which I believe is
this code:
    this.offsetParent = this.helper.offsetParent(); var po =
this.offsetParent.offset();
The developer who did our sort implementation seems to have gone
inactive, so any help that someone might provide would be great.
What sort of changes from 1.5.3 to 1.6 might be behind this failure
and what should we be doing differently to avoid it?