Column names in C#

Hello, I made an Excel spreadsheet a datatable and I am trying to get information from the columns via using a column name in C#.  The problem I am having is my C# error says that the column does not belong in the table.  So what kind of format issue am I having?

for (int j = 0; j < dt.Rows.Count; j++)
                {
                    //GroupName1 GroupName2 GroupName3 Snd_Nbr Rcv_Nbr Snd_Size Rcv_Size PartnerTypeName Id_Recipient Id_Regroup SelRecip
                    string sql = "";
                    sql =
                        "insert mpExchangeActivityByUser " +
                        "select " + MP.Database.Utils.FxQs(dt.Rows[j]["Snd_Nbr"].ToString(), "'") + ", " +
                        "       " + MP.Database.Utils.FxQs(dt.Rows[j]["Snd_Size"].ToString(), "'") + ", " +
                        "       " + MP.Database.Utils.FxQs(dt.Rows[j]["SelRecip"].ToString().Replace("\"", ""), "'") + ", " +
                        "       " + MP.Database.Utils.FxQs(senddate.ToShortDateString(), "'") + " ";

                    dbu.ExecuteNonQuery(sql);
                    sql = "";
                }

Select allOpen in new window