function custom_form_alter(&$form, &$form_state, $form_id) {

global $user;
$node = node_load(arg(1));
$num  = $node->field_node_reference['und'][0]['nid'];
$val  = node_load($num);
$event_noderef_uid = $val->uid;



if($form_id == 'regester_node_form'){

if($user->uid == $event_noderef_uid){
 $form['field_NAME']['#access'] = FALSE;
 }