[fw-mvc] Exception with HeadLink

I recently upgraded some code from 1.6.x series to 1.7.5 and came up
with some issues related to the HeadLink view helper.

I get the following:
Fatal error: Call to undefined method
Zend_View_Helper_Placeholder_Container::ksort() in
/export/home1/webapps/***/library/Zend/View/Helper/HeadLink.php on
line 310

In my Controller I have:

$this->view->headLink()->appendStylesheet($this->basePath.'/public/css/k_style_cs.css');
$this->view->headLink()->appendStylesheet($this->basePath.'/public/css/k_print_cs.css',
'print');
$this->view->headLink()->appendStylesheet($this->basePath.'/public/css/style.css');
$this->view->headLink()->appendStylesheet($this->basePath.'/public/css/IE7styles.css',
"screen", "(IE 6)|(IE 7)");

and the layout.phtml I have:

<?= $this->headLink() ?>

Any ideas?

Regards,
Jay M. Keith