Old Pitch Theme

Hi –

We are using the PITCH theme on the site at yigp.org. A few days ago we noticed the below error code which shows up on the front end of the website. Any ideas on how this would suddenly occur and how to resolve the issue?

Warning: Declaration of Pitch_Walker_Page::start_el(&$output, $page, $depth, $args, $current_page = 0) should be compatible with Walker_Page::start_el(&$output, $page, $depth = 0, $args = Array, $current_page = 0) in /home/ptrail/public_html/wp-content/themes/pitch/functions.php on line 435

Thanks!