The stored procedure doesn't work fine when inserted condition for date

Question

Hi,
I have a stored procedure which when not inserted the row for date calculates correctly, but with it, the sp just takes the last enrtered value for saldo, instead of performing the calculation.  Here is the sp:

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 and vp>=0 and vp<=10

select @isplata = sum(iznosden)
from blagajna_jspturs
where vp>10 and data=@data

set @saldo = isnull(@saldo,0) + (isnull(@priem,0)) - (isnull(@isplata,0))

update Kasovizvestaj

set 
 idki=@idki,
 saldo=@saldo
 where data=@data   ---this row is the problem

select saldo from Kasovizvestaj
return

Can anybody help me please? Thanks