Datepicker box generally stop working due to change in Jquery-ui and jquery version. Tough our system is saturated with the script, If we update jquery version. Many other api would become invalid so It was better to fix the bug which was :
There is a "Class" in Calander Div name ""ui-helper-hidden-accessible" Find and remove this class from
[website]/js/jquery.datepicker.js
 and datepicker will then continue working.