Sqldatareader problem with the application

private void view_list_User_DDL()
        {
            try
            {
                //نمایش جدول کاربران
                if (scon.State == ConnectionState.Closed)
                    scon.Open();
                SqlDataAdapter sda = new SqlDataAdapter("Select_User_DDL", scon);
                sda.SelectCommand.CommandType = CommandType.StoredProcedure;
                DataTable dt = new DataTable();
                sda.Fill(dt);
                comboBox2.DataSource = dt;
                comboBox2.DisplayMember = "l_name";
                comboBox2.ValueMember = "id_user";
            }
            catch (Exception err)
            {
                MessageBox.Show("ERROR" + err, "اخطار", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
            finally
            {
                scon.Close();
            }
        }

private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            try
            {
                //نمایش نام کاربر
                if (scon.State == ConnectionState.Closed)
                    scon.Open();
                SqlCommand scm = new SqlCommand("Select_Lname_Fname", scon);
                scm.CommandType = CommandType.StoredProcedure;
                scm.Parameters.AddWithValue("@id_user", comboBox2.SelectedValue);
                SqlDataReader sdr = scm.ExecuteReader();
                if (sdr.HasRows)
                {
                    sdr.Read();
                    label10.Text = sdr[0].ToString();
                    sdr.Close();
                }
            }
            catch (Exception err)
            {
                MessageBox.Show("ERROR" + err, "اخطار", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
            finally
            {
                scon.Close();
            }
        }

ERRORSystem.ArgumentException: No mapping exists from object type System.Data.DataRowView to a known managed provider native type.
   at System.Data.SqlClient.MetaType.GetMetaTypeFromValue(Type dataType, Object value, Boolean inferLen, Boolean streamAllowed)
   at System.Data.SqlClient.SqlParameter.GetMetaTypeOnly()
   at System.Data.SqlClient.SqlParameter.Validate(Int32 index, Boolean isCommandProc)
   at System.Data.SqlClient.SqlCommand.SetUpRPCParameters(_SqlRPC rpc, Int32 startCount, Boolean inSchema, SqlParameterCollection parameters)
   at System.Data.SqlClient.SqlCommand.BuildRPC(Boolean inSchema, SqlParameterCollection parameters, _SqlRPC& rpc)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader()
   at ShafieiNan.Sel.comboBox2_SelectedIndexChanged(Object sender, EventArgs e) in C:\Users\PCTirTash\documents\visual studio 2010\Projects\ShafieiNan\ShafieiNan\Sel.cs:line 292