Closed Unassigned: Issue with modal popup extender with tab container [27801]

I have a ModalPopupExtender that I am using to popup a panel that contains a TabContainer with some TabPanels. After upgrading to the new toolkit when I click the button to popup the panel with the tabs I am getting a javascript error:

______Unable to get property 'length' of undefined or null reference______

This never happened before. Any idea what could be the cause? Or if there is a fix for this?
Comments: Merged with item [27775](https://ajaxcontroltoolkit.codeplex.com/workitem/27775).