Getting Combobox Selected Value Given Error

BusinessLayer blayar = new BusinessLayer();
            DataTable dt = blayar.getproductType(Global.CompanyId);
            cmbProType.DataSource = dt;
            if (dt.Rows.Count > 0)
            {
                cmbProType.DisplayMember = "Type";
                cmbProType.ValueMember = "id";
                cmbProType.DataBind();

            }

private void cmbProType_SelectedIndexChanged(object sender, EventArgs e)
        {
            bType = true;
            if (bType)
            {
                int counter;
                int id_ProductType=Convert.ToInt32(cmbProType.SelectedValue);// Getting  Error IConvetable System.row.RowDataView like this 
                BusinessLayer blayer = new BusinessLayer();
                DataTable dt = new DataTable();
                counter = blayer.ChecksubTypeofType(id_ProductType);
                if (counter > 0)
                {
                    dt = blayer.getProductSubtype(id_ProductType);
                    if (dt.Rows.Count > 0)
                    {
                        cmbProdSubType.DataSource = dt;
                        cmbProdSubType.DisplayMember = "Type";
                        cmbProdSubType.ValueMember = "id";
                         cmbProdSubType.DataBind();
                    }
 
                }
                else
                {
                    dt = blayer.getProductByTypeID(id_ProductType);
                    DGviewList.DataSource = dt;
                    DGviewList.DataBind();
                 
                }
            }
            else
                bType = false;
        }