UPDATE
I have reverted back to Jquery 1.3.2 and everything is working, not sure what the problem is/was as I have not changed anything else apart of t
I've had a similar issue with 1.7.2 versions of jQuery and jQuery UI. The popup wasn't showing up and none of the applicable suggestions above helped. What helped in my case was taking out the class="hasDatepicker" which (as the accepted answer here notes: jQuery UI datepicker will not display - full code included) is used by jquery-ui to indicate that a datepicker has already been added to the text field. Wish I found that answer sooner.