What is wrong with this code

[Mirnes]

Yes, a problem is with that line of code, that's sure. But, I use try...catch only to see what is going on. Actually, I'm going to use this code:

Dim StopeRedak As DataRow = Me.NarudzbeKupacaDataSet.Tables("SifarnikArtikli_StopePoreza").Rows.Find(StopaId)
            If StopeRedak IsNot Nothing Then
                DefStopa = StopeRedak("StopaStopa")                 
                NarudzbeKupacaStavkeDgr.Rows(e.RowIndex).Cells("PdvStopa").Value = DefCijena
            End If

If I put Msgbox(StopaId) in front of this code, I got message that value of that variable is 7. So, I checked and there is record in SifarnikArtikli_StopePoreza with Id=7 and that table existing in NarudzbeKupacaDataSet. Also, there is column StopaStopa in that table and also there is column PdvStopa in Datagrid NarudzbeKupacaStavkeDgr. I checked names some 50 times and values and all of small possibilities that could go wrong but everything is OK. So, what else could be wrong? I really need some help above this, I stuck with it for few days and this part is crucial for my project, I can't go further with it until I solve this.