If you are using the jQuery ui framework and the datepicker you may get from time to time the error uncaught exception: Missing instance data for this datepicker. Your jquery looks something like this (it's a working example)
<script type="text/javascript"><br />$("#datepicker").datepicker({dateFormat: "yy-mm-dd", <br /> constrainInput: true, // prevent letters in the input field<br /> autoSize: true, // automatically resize the input field <br /> altFormat: "yy-mm-dd", // Date Format used<br /> firstDay: 1 // Start with Monday<br />});<br /></script>
all the necessary files (javascript and CSS) are included and there is a textfield with the id datepicker.
However the error still appears. Some fixs to the problems can be found here, here and here, but if everything is ok and script still not working you can consider turning off Firebug (the plugin design for Firefox): when active and running, the Firequery can interfere with jQuery and stop it from running.
