zend can't send Last-Modified header - zend-framework

Question

I try to send Last-Modified header. I can see it when run project on local computer but when I run copy of it on virtual host there is no Last-Modified header.
class InfoController extends Zend_Controller_Action
{
public function indexAction(){
$arr = strip_tags($this->_getParam('link'));
$material = new Application_Model_InlineMenus();
$mat = $material->preparematerial($arr);
$header= $this->getResponse()->setHeader("Last_Modified", gmdate("D, d M Y H:i:s", strtotime($mat['created']))." GMT", true);
//other parts of code
}
}
This is what I have in firebug when run project on local machine
Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Connection Keep-Alive
Content-Length 4563
Content-Type text/html
Date Fri, 15 Feb 2013 10:31:49 GMT
Expires Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive timeout=5, max=99
Last-Modified Thu, 14 Feb 2013 12:41:31 GMT
Pragma no-cache
Server Apache/2.2.22 (Win32) PHP/5.3.13
X-Powered-By PHP/5.3.13
And this is what I've got on my hosting
Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Connection keep-alive
Content-Encoding gzip
Content-Type text/html; charset=UTF-8
Date Fri, 15 Feb 2013 10:34:06 GMT
Expires Thu, 19 Nov 1981 08:52:00 GMT
Pragma no-cache
Server nginx/1.1.10
Transfer-Encoding chunked
X-Powered-By PHP/5.3.21
There is a single difference between local project and real project - I use .htaccess in www directiory to redirect requests to www/public directory.
UPD. I created plugin and in preDispatch() tried to set header and I've got http-code 500
Problem solved: disable SSI