Marie Comet

Okay solved by myself :
If intersted someone, you need to change this

function gmw_state_filter( $clauses, $gmw ) {

  global $wpdb;

  /*
   * we first do a form check to make sure we only filter the search form that we want.
   * for this example I will use form with ID 1
   */
  if ( $gmw['ID'] != 1 )
       return $clauses;

  /*
   * check if a state value exists.
   * everytime the state value exists in URL the search query below will take over
   * and filter results  based on that state.
   * That is the reason we keep giving the states select box the deafult value on page load.
   * To preven visitors from having to manually change it back to deafult when
   * they want to do a proximity search based on address instead of state
   */
   if ( !isset( $_GET['gmw_state'] ) || empty( $_GET['gmw_state'] ) )
    return $clauses;

  //get the sate value from URL
  $state_value = $_GET['gmw_state'];

  //filter the tables clauses
  $clauses['fields']  = " wp_posts.*, gmwlocations.* ";

  //filter the WHERE cluase to look for locations with based on thier  state
  $clauses['where'] .= $wpdb->prepare(" AND gmwlocations.state_long = %s", $state_value );

  $clauses['groupby'] = "$wpdb->posts.ID";

  //order results by state name since we cannot orde rby distance
  $clauses['orderby'] = "$wpdb->posts.post_title"; 

  return $clauses;

}
add_filter( 'gmw_pt_location_query_clauses', 'gmw_state_filter', 99, 2 );

By :

function gmw_state_filter( $clauses, $gmw ) {

  global $wpdb;

  /*
   * we first do a form check to make sure we only filter the search form that we want.
   * for this example I will use form with ID 1
   */
  if ( $gmw['ID'] != 1 )
       return $clauses;

  /*
   * check if a state value exists.
   * everytime the state value exists in URL the search query below will take over
   * and filter results  based on that state.
   * That is the reason we keep giving the states select box the deafult value on page load.
   * To preven visitors from having to manually change it back to deafult when
   * they want to do a proximity search based on address instead of state
   */
   if ( !isset( $_GET['gmw_state'] ) || empty( $_GET['gmw_state'] ) )
    return $clauses;

  //get the sate value from URL
  $state_value = $_GET['gmw_state'];

  //filter the WHERE cluase to look for locations with based on thier  state
  $clauses['where'] .= $wpdb->prepare(" AND gmwlocations.state_long = %s", $state_value );

  return $clauses;

}
add_filter( 'gmw_pt_location_query_clauses', 'gmw_state_filter', 99, 2 );

Solved.