>no, the code of stored procedure has not been changed, here is the code
>
>

>ALTER PROCEDURE [dbo].[P_ANALISIS]@fecha1 varchar(10),@fecha2 varchar(10),@escolar int,@tipmov varchar(2),@nivel int,@dias int,@cuota int
>AS
>BEGIN
>DECLARE @ParmDefinition NVARCHAR(2000),@condi varchar(2000),@sql nvarchar(4000)
>SET @ParmDefinition = N'@fecha1 varchar(10),@fecha2 varchar(10),@escolar int,@tipmov char(2),@nivel int,@dias int,@cuota int'
>set @sql='select rtrim(F.apellidos) as apellidos,
>SUM(M.balance) as balance,SUM(M.cuota) as monto,SUM(m.recargo) as recargo,0 as anticipo,
>descuentos=sum(CASE WHEN (@fecha1>m.fechadescuento) THEN 0 else (M.descuento+M.descuento2) END),
>dias30=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)<=30 and @fecha1>=m.fechacuota) THEN m.balance else 0 END),
>dias45=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)> 30 and  datediff(dd,m.fechacuota,@fecha1)<= 45)  THEN m.balance else 0 END),
>dias60=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)> 45 and  datediff(dd,m.fechacuota,@fecha1)<= 60)  THEN m.balance else 0 END),
>dias75=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)> 60 and  datediff(dd,m.fechacuota,@fecha1)<= 75)  THEN m.balance else 0 END),
>dias90=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)> 75 and  datediff(dd,m.fechacuota,@fecha1)<= 90)  THEN m.balance else 0 END),
>dias91=sum(CASE WHEN (datediff(dd,m.fechacuota,@fecha1)>=91) THEN m.balance else 0 END)
>from cuotas m,familias f 
>where M.idfamilia=f.idfamilia and M.balance>0 '
>
>IF @fecha1 IS NOT NULL and LEN(@Fecha1) > 0
>        SET @condi = @condi +'   AND m.fechacuota>= @fecha1'
>
>IF @fecha2 IS NOT NULL and len(@Fecha2) > 0
>        SET @condi = @condi +'   AND m.fechacuota<= @fecha2'
>
>IF @escolar <> 0  and @escolar IS NOT NULL
>        SET @condi = @condi +'   AND m.escolar= @escolar'
>
>IF @tipmov != ''
>        SET @condi = @condi +'   AND m.tiptra= @tipmov'
>
>IF @nivel <>0 and @Nivel IS NOT NULL
>        SET @condi = @condi +'   AND m.nivel= @nivel'
>
>IF @dias <>0 and @dias IS NOT NULL
>        SET @condi = @condi +'   AND m.dias= @dias'
>
>IF @cuota <>0 and @cuota IS NOT NULL
>        SET @cuota = @condi +'   AND m.cuota= @cuota'
>
>set @sql=@sql+ @condi + 'group by M.idfamilia,F.apellidos'
>
>EXECUTE sp_executesql @sql,@ParmDefinition,@fecha1,@fecha2,@escolar,@tipmov,@nivel,@dias,@cuota
>
>

I don't see where you initialized the @Condi. When you're debugging an SP, you need to add PRINT @SQL to verify if the @SQL is correct. I suspect in your case it will be NULL if the @Condi variable is not initialized.