when run my code I got this error "Parameters were not supplied for function"

[Gilberto16]

 SqlDataAdapter dam = new SqlDataAdapter("select * from calculate_amt where DistrictName='" + DropDownList1.Text + "' and poste='" + DropDownList2.Text + "'", con);
            DataSet dsm = new DataSet();
            dam.Fill(dsm, "amt");
            DataView dvm = new DataView(dsm.Tables["amt"]);
            txtAmt.Text = dvm[0]["amt"].ToString();