Comment on WordPress Custom Nav Menu by Rich.

WordPress Drop Down Menu Hi there
I have just uploaded the new version and activated it on my chosen wp site.

After entering my Tran code I went to view the front page and saw the following error message
Dont know what it means or how to fix it;

Fatal error: Call to undefined function get_post_format() in /home/acoach5u/public_html/selfimprovementmastery/wp-content/themes/stallion-seo-theme/index.php on line 30
Can you assist?

Thank You