I've updated recently from Moodle 2.6.2 to 2.8.5, and I'm having some troubles. When I'm editing a course, the expandibles actions don't work, I've attached how old Moodle was working and how works the new one.
The firebug console drops:

>TypeError: t is undefined
>
>
>...00px",showPrevMonth:!0,showNextMonth:!0,firstdayofweek:t.firstdayofweek,WEEKDAYS...
>
>
>http://BASE_URL/theme/yui_combo.php?m/1426165440/form/dateselector/dateselector-min.js (línea 1, col 1490)

I've AJAX enabled, and also I've tried using fastcgi module (in some forum make mention of fastcgi problem related)

What could it be?