DateTime无法打开

I have a problem with my DateTime function.

I'm using a 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 I use this function for adding a new event in my fullcalendar its works fine. But my problem is when I try to use it for an update to the calendar and it says

Warning: require(libs/DateFormat.php): failed to open stream: No such file or directory in /Applications/MAMP/htdocs/coach/index.php on line 12

I have no such a file in my libs directory as it is from php.

any one knows ho to get this working?

Thanks for the help