This error message appears in the search with no search parameter, because mb_strpos has an empty second parameter.

I fixed this as follows, though I'm not sure of the implications. Can someone tidy this up and add it to Joomla if you see fit.

if ( $offset === FALSE ) {

    // 22-nov-2014 Greg check search for being empty to avoid Delimiter Empty error
    if(strlen($search) > 0) {
        return mb_strpos($str, $search);
    }
    else {
        return 0;
    }

} else {
    return mb_strpos($str, $search, $offset);
}