Update quantity on sales line via Web Service and PHP

Hello

I am trying to transfer sales orders from Magento to Navision (2009 SP1). I'm doing it through Web Services and PHP code . The order is created correctly, but the quantity field is not updated . Does anyone have an idea?. My code is this :

- Creating order line:
$ order_line = 'Order ';
$ order_line = $ order_info [" increment_id "] ;
$ order_line = $ linea_pedido ;
$ order_line = 'Item' ;
$ order_line = $ no_producto ;

$ linea_pedido_insertar = array (' Linea_Pedido ' = > $ order_line );

$ pagelineapedidos -> Create ($ linea_pedido_insertar );

Updating the Sales Line Record

$ linea_mod_pedido - > Linea_Pedido - > Variant_Code = $ cod_variante ;
$ linea_mod_pedido -> Linea_Pedido -> PfsOrder_Quantity = number_format ($ lineapedido , 2);
$ linea_mod_pedido -> Linea_Pedido -> Location_Code = Mage :: helper (' navisionconect ') -> getDataWeb ( ' stock ', ' data_conf ');
$ linea_mod_pedido -> Linea_Pedido - > Cantidad = 99 ;
$ linea_mod_pedido -> Linea_Pedido -> CantidadSpecified = true ;
$ linea_mod_pedido -> Linea_Pedido -> UNIT_PRICE = $ price;

$ pagelineapedidos -> Update ( $ linea_mod_pedido );


I created the "cantidad" field to test , but not updated in Navision.

Thanks in advance.