I have been using datepicker in the jQuery UI package for quite a while and it was always nice and easy, until this morning when I was trying to add it to a page, it keep giving me the error "$(".datepicker").datepicker is not a function". I check from firbugs that, the jquery-ui-1.7.2.min.js is included, so as the jquery-1.3.2.min.js. I was copying the code from another page I wrote, where the datepicker works just well. I was haunting around that several lines of code, trying to use other version of jQuery and jQuery UI, but found nothing, until I roll down to the page and saw that there is another script reference of jquery-1.3.2.min.js, which I added 2 days ago for other purpose. As soon as I remove that second include, the datapicker come back to life.