ForeignKeyConstraint Erros

Hi... I have  related table and I have ForeignKeyConstraint so when I delete parent table's data, 
child table's related data don't delete.
After this I  re Run project An occurs Error. My code is like  below . thank you...

  void iliskilendir( )

       {

           try

           {

               string sorgu_firma = "select * from firma";

               string sorgu_bocek = "select * from bocek_veri";

 

               adpt_firma = new OleDbDataAdapter(sorgu_firma, baglan());

               adpt_bocek = new OleDbDataAdapter(sorgu_bocek, baglan());

               ds = new DataSet();

 

               adpt_firma.Fill(ds, "firma");

               adpt_bocek.Fill(ds, "bocek_veri");

 

               DataColumn firma_kolon = ds.Tables["firma"].Columns["firma_ID"];

               DataColumn bocek_kolon = ds.Tables["bocek_veri"].Columns["firma_ID"];

 

               ForeignKeyConstraint kisitla = new ForeignKeyConstraint(firma_kolon, bocek_kolon);

               kisitla.UpdateRule = Rule.Cascade;

               kisitla.DeleteRule = Rule.Cascade;

               kisitla.AcceptRejectRule = AcceptRejectRule.Cascade;

 

               ds.Tables["bocek_veri"].Constraints.Add(kisitla);

               ds.EnforceConstraints = true;

 

 

               vt_iliski = new DataRelation( "firma_To_bocek_veri" , firma_kolon, bocek_kolon,true );

 

 

            

               ds.Relations.Add(vt_iliski);

              

 

 

               yonet_firma = new BindingSource(ds, ds.Tables["firma"].ToString());

               yonet_bocek = new BindingSource(yonet_firma, "firma_To_bocek_veri");

             

 

               // TextBoxlar firma tablosunun alanlarina baglaniyor          

               firma_IDTextBox.DataBindings.Add("Text", yonet_firma, "firma_ID");

               firma_adiTextBox.DataBindings.Add("Text", yonet_firma, "firma_adi");                                             firma_iliTextBox.DataBindings.Add("Text", yonet_firma, "firma_ili");

               firma_telTextBox.DataBindings.Add("Text", yonet_firma, "firma_tel");                                             firma_adresiTextBox.DataBindings.Add("Text", yonet_firma, "firma_adresi");

               firma_is_tanimiTextBox.DataBindings.Add("Text", yonet_firma, "firma_is_tanimi");

               kayit_tarihiDateTimePicker.DataBindings.Add("text", yonet_firma, "kayit_tarihi");

 

               adpt_firma.Dispose();

               adpt_bocek.Dispose();

              

           }

           catch (Exception hata)

           {

               MessageBox.Show("Hata 3 olustu :" + hata.TargetSite  );       }      }