Thanks to everybody!!!; I was testing this script in SQL Server 2005 and everthing is ok.

//>>>>

DECLARE @lValueStr VARCHAR(MAX)

SET @lValueStr = NULL

SELECT @lValueStr = COALESCE(@lValueStr + ', ', '')

+ a.Cod_Asignatura + '(' + CAST(rtrim(ltrim(b.Des_Asignatura)) AS VARCHAR(30)) + ')'

FROM pla_tt_PlanificacionDetAsig a inner join pla_tc_Asignatura b

on a.cod_empresa = b.cod_empresa

and a.cod_recinto = b.cod_recinto

and a.cod_asignatura = b.cod_asignatura

SELECT @lValueStr

<<<<//

I Really don't understan how it work, but just work and good! 🙂 :w00t:

Best regards.