Sorting on multiple columns in Sonata Admin

http://www.phpassionate.com/2013/02/06/sorting-on-multiple-columns-in-sonata-admin/

Catchable Fatal Error: Object of class DateTime could not be converted to string

If you end up with the following error – An exception has been thrown during the rendering of a template (“Catchable Fatal Error: Object of class DateTime could not be converted to string”) – you probably forgot to install or enable SonataIntlBundle: new Sonata\IntlBundle\SonataIntlBundle(), in AppKernel.php.