ı can't integrate ajax with my form

function maliyet_poz_ara_form(){
$form['#method']='post';
$form['kriter'] = array(
    '#type' => 'fieldset',
    '#title' => t('Poz Arama Kriterleri'),
    '#tree' => TRUE,
  );
$form['kriter']['fmetin'] = array(
    '#type' => 'textfield',
    '#title' => t('Name'),
    '#size' => 30,
    '#maxlength' => 64,
    '#description' => t('Enter the name for this group of settings'),
  );

  $form['kriter']['submit'] = array(
  '#type' => 'submit',
  '#value' => t('Search'),
  );
return $form;
}

function maliyet_poz_form_alter(&$form, $form_state, $form_id){
 if ($form_id == 'maliyet_poz_ara_form') {
  //Set form to work with ajax
  $form['#ajax'] = array(
  'enabled' => TRUE
  );
  }
}

But an alert appearing when I submit form. ajax.module:An unknown error has occured.
in the html code:
<form action="/maliyet/pozara" accept-charset="UTF-8" method="post" id="maliyet-poz-ara-form" class="ajax-form">
<input type="submit" name="op" id="edit-kriter-submit" value="Ara" class="form-submit ajax-trigger" />

form action url is the same url with the form. Is it problem?