The problem is that IE9 now adheres to standards, and this creates problems with plugins trying to work around problems before IE9.
One possible solution is to force IE9 to turn on in IE8 standards mode using this meta tag:
<meta http-equiv="X-UA-Compatible" content="IE=8"></meta>
Another option is to fix the code:
most user interface plugins are on $.browser.msie
to check if we are in IE, but they do not check the version. In my case, the solution (jquery.ui.checkbox.js) was to replace all calls to $.browser.msie
this variable:
var isIEAndVersionIsLowerThan9 = $.browser.msie && (parseInt($.browser.version, 10) < 9);
This solution is better than adding a meta tag because it will allow you to use all the features of IE9.
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