empty delimiter error – help please?

wordpress suddenly started taking forever to accept a post.
i looked at my error log in CPanel and this is there 20+ times today-

[14-Jun-2005 13:30:43] PHP Warning: strpos(): Empty delimiter. in /home/twowiths/public_html/wp-includes/classes.php on line 684

i found the classes.php file and pasted the code for line 684 below- can anyone tell me what’s wrong? any help would be greatly appreciated. thank you.

683 function find_spam() {
684 $in_queue = 0;
685
686 foreach( $this->comment_list as $comment ) {