Saving multiple checkboxes using PHP-jQuery to MSSQL Server

I am trying to save a record in to MSSQL server data base from multiple checkboxes using PHP-jQuery

But this error appears.

The problem is in PHP code, how to read this string and record this data in MSSQL DB?

if(isset($_POST['buttonsave']))
{  //echo "bttnsave"; // Mensaje Afirmativo.
            $vfpg   = $_POST['perGrupo'];
            $vfdg   = $_POST['depGrupo'];
            $vfsg   = $_POST['selGrado'];
            $vfchs  = $_POST['myCheckboxes']; // Array secciones A,B,C,..

            $query_in="INSERT INTO igrupos (idperiodo, idcarrera, grado, seccion)
                                           VALUES (?,?,?,?)";
        for ( $i=0; $i < count( $vfchs ); $i++ )
    {
        // do some stuff, save to database, etc.
         $params = array( 
                          array($vfpg   ,SQLSRV_PARAM_IN),
                          array($vfdg   ,SQLSRV_PARAM_IN),
                          array($vfsg   ,SQLSRV_PARAM_IN),
                          array($vfchs  ,SQLSRV_PARAM_IN)   

                         );
    }                                      

            $sql_in = sqlsrv_query($conn,$query_in,$params);
          if ($sql_in) // Se eejectuto la sentencia SQL?
           {
             echo "SQLSuccess"; // Affirmative message.

            } else {
     $msgErrorSQL = "Error SQL not working"; // Negative Message;                     

              die( print_r( sqlsrv_errors(), true)); // Causa del error.          
                    }
             exit();
        }

Thanks a lot!