draggable in IE9

draggable in IE9

I have an app that uses draggables, and it's not working in IE9.  Either jquery 1.3.2 or 1.4.2 (no difference) and UI 1.7.2.  I see the posts about the UI needing to be upgraded.  Upgrading UI is fine, and this does solve the problem.

However, I have a separate app that also uses draggables, and is also on jquery 1.4.2 and UI 1.7.2, and its draggables work fine in IE9.  I'd like to narrow down what the difference is, so that I'll know that the issues with the first app are truly fixed, and whether or not the second needs to be upgraded, even though it's working fine.  There must be an additional factor that stops the draggable from working in one, but not in the other?

Thank you.