Error message on several blog posts

Hi

This error message comes up on a few links how can i fix it and check its not happening on other pages?

Fatal error: Call to a member function getType() on a non-object in /home/blatantl/public_html/plugins/system/sef/sef.php on line 38

e.g. http://www.blatantlyblunt.com/Blog/billy-danze-m-o-p-on-touring-with-gangstarr-street-certified-and-more.html

thanks