February 26, 2013 at 17:16 /
There’s a access error to your admin-ajax.php.
Try to save your permalink setting again.
Do you have any plugins installed that mess with the access to admin?
Or maybe it’s something wrong in your .htaccess
This could help you
http://wordpress.org/support/topic/upgrade-to-22-dashboard-not-working?replies=36
Regards