Ray's Asp.net Blog: How to solve problem, jQuery UI datepicker not working in IE9?

http://rayaspnet.blogspot.ca/2011/12/how-to-avoid-quirks-mode-in-ie.html

Put this line into the first place
<head>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
</head>

or set this meta tag in IIS server into HTTP response headers.

Reference:
How to avoid compatibility view and quirk mode in IE?