How to resolve cannot find table 0 error in binding combo box using three tier architecture

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C#

when i post my bind method in form load event it shows cannot find table 0 error.
also when i bind single combo box its working but when i bind more than one combo box its shows error.

What I have tried:

DAL part is.............

public DataSet prno_combo(SqlCommand cmd)
        {
            DataSet ds = new DataSet();

           
                getcon();
                cmd.Connection = getcon();
                SqlDataAdapter adapt = new SqlDataAdapter(cmd);
                adapt.Fill(ds, "Purchase");
                DataRow dr = ds.Tables[0].NewRow();
                dr["Id"] = "Select";
                dr["Id"] = "0";
                ds.Tables[0].Rows.InsertAt(dr, 0);                             
                return ds;

}

 public DataSet store_combo(SqlCommand cmd)
        {
            DataSet ds = new DataSet();
            
                                 
                        getcon();
                        cmd.Connection = getcon();
                        SqlDataAdapter adapt = new SqlDataAdapter(cmd);
                        adapt.Fill(ds, "StoreMaster");
                        DataRow dr = ds.Tables[0].NewRow();
                        dr["StoreName"] = "Select";
                        dr["id"] = "0";
                        ds.Tables[0].Rows.InsertAt(dr, 0);
                        return ds;
                }

BL part is..............

public DataSet BL_prno_combo(clsPRml mlprobj)
       {
           SqlCommand cmd = new SqlCommand();
           cmd.CommandType = CommandType.StoredProcedure;
           cmd.CommandText = "Prc_BindPurchaseMandate";
           return dlprobj.prno_combo(cmd);
       }

       public DataSet BL_store_combo(clsPRml mlprobj)
       {
           SqlCommand cmd = new SqlCommand();
           cmd.CommandType = CommandType.StoredProcedure;
           cmd.CommandText = "Prc_BindStore";
           return dlprobj.store_combo(cmd);

Form of presentation part is......

public void BindPRnoCombo()
       {

               cbPRNo.DataSource = blprobj.BL_prno_combo(mlprobj).Tables[0];
               cbPRNo.ValueMember = "Id";
               cbPRNo.DisplayMember = "Id";
               cbPRNo.SelectedIndex = 0;


       }


       public void BindStoreCombo()
       {

               // ERROR OCCURS HERE
               cbStore.DataSource = blprobj.BL_store_combo(mlprobj).Tables[0];
               cbStore.ValueMember = "Id";
               cbStore.DisplayMember = "StoreName";
               cbStore.SelectedIndex = 0;