Cita:
Iniciado por Libras 
y como esta tu trigger(codigo)??
ALTER TRIGGER [dbo].[trg_Periodo1]
ON [dbo].[Periodo]
AFTER INSERT
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for trigger here
update Alumno set
AlumnoNuevo = 0
where AlumnoNuevo = 1
END