php - DateTime failed to open -

i have problem datetime function.

i'm using function form different places

function newdateformat($date, $format) {    $newdate = new datetime($date);   if($format == '1')   {      $newdate = $newdate->format('y-m-d h:i:s');    }elseif($format == '2'){      $newdate = $newdate->format('y-m-d');   }   return $newdate;} 

when use function adding new event in fullcalendar works fine. problem when try use update calendar , says

warning: require(libs/dateformat.php): failed open stream: no such file or directory in /applications/mamp/htdocs/coach/index.php on line 12

i have no such file in libs directory php.

any 1 knows ho working?

thanks help