PHP - Ajax调用 - <b>致命错误</ b>：在非对象上调用成员函数prepare（）

My website is currently in French, English and Dutch. French is the main language and the only one working up to now.

My jquery script makes an ajax call to a php page.

The response I got is this one : Fatal error: Call to a member function prepare() on a non-object in

How can I get rid of this error ? On the french version it works perfectly ! The 3 languages uses the same php script.

fermetureEtablissement = [] ;

$.ajax({
    type: "POST", 
    url: "./admin/datesajax.php", 
    data: ({idproduit: 'tous'}), 
    cache: false, 
    dataType: "json", 
    async: false, 
    success: function(data) {
        fermetureEtablissement = data;
    }
}); 

Do you have any idea how to fix this problem ?

You can see the not working page here :

1. Click on "book" on this page : http://www.velo-montagne.com/en/hotel/au-colombier-de-luxe-room
2. Then check the ajax call and the response. It shows the error.

You can see the working page here :

1. Click on "reserver" on this page : http://www.velo-montagne.com/hotel/chambre-au-colombier-de-luxe
2. Then check the ajax call and the response. It works great !

Example of dateajax.php :

if ($_POST['idproduit'] == 1 or $_POST['idproduit'] == 4 or $_POST['idproduit'] == 5 or $_POST['idproduit'] == 'tous' or $_POST['idproduit'] == 'ouverturesexceptionnelles' ){  
    $sth1 = $dbh->prepare("SELECT datesbloquees FROM vm_datesbloquees WHERE idproduit = :idproduit" );
    $sth1->execute(array(':idproduit' => $_POST['idproduit'])); 
    $result = $sth1->fetchAll();

    $tableaudatesbloquees = explode(",", $result[0]['datesbloquees']);
    //print_r($tableaudatesbloquees);
}


function dbConnect(){
  global $dbh;

  $dbInfo['database_target'] = "xxx";
  $dbInfo['database_name'] = "xxx";
  $dbInfo['username'] = "xxx";
  $dbInfo['password'] = "xxx";

  $dbConnString = "mysql:host=" . $dbInfo['database_target'] . "; dbname=" . $dbInfo['database_name'];
  $dbh = new PDO($dbConnString, $dbInfo['username'], $dbInfo['password'],array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES \'UTF8\''));
  $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

}

The variable $dbh does not contain the database object