Sidebar issue – warning message

An issue popped up today though no changes were applied on the site:

On the right sidebar, a warning message on the home page:

Warning: preg_replace() [function.preg-replace]: Unknown modifier ‘<‘ in /home/content/90/5110390/html/wp-content/plugins/page-links-to/page-links-to.php on line 186

Assuming this is the code it refers to:

if ( $highlight ) {
		$pages = preg_replace( '| class="([^"]+)current_page_item"|', ' class="$1"', $pages ); // Kill default highlighting
		$pages = preg_replace( '<li class="([^"]+)"><a href="' . $current_page . '"', '<li class="$1 current_page_item"><a href="' . $current_page . '"', $pages );