Problem with the stored procedure

Question

Hi,
I have this stored procedure:

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER procedure [dbo].[presmetajSaldo]
(
@idki int,
@data DateTime,
@saldo numeric(12,3) output
)
as
Declare @priem numeric(12,3) 
Declare @isplata numeric(12,3)

select @priem = sum(iznosden) from blagajna_jspturs
where data=@data
set @saldo = isnull(@saldo,0) + (isnull(@priem,0)) - (isnull(@isplata,0))
update Kasovizvestaj
set 
 saldo=@saldo
where data=@data

select saldo from Kasovizvestaj
return

When I erase the bold row, the sp calculates correctly, but when I put that row in the sp, it doesn't calculates. Without select saldo from Kasovizvestaj row, it throughs a message "0 rows affected".
Can anybody help me please with a suggestion what's wrong with my sp?

I also tried with:

where CONVERT(VARCHAR(10),data,104) =  CONVERT(VARCHAR(10),@data,104)

instead of
where data=@data

but without success.

Thanks a lot in advance.