C# DataTable Row SetField Error: Cannot set column 'Excess'. The value violates the MaxLength limit of this column.

i having a probelm editing data on a datatable . i have loaded data into a datatable and some clounms got null value which i placed that in an on the SP now i want to edit some clounms in the datatble

dt1 = AuthWorkdone.View_AuthorsationReport_WorkDone1(DateTime.Parse(txtStart.Text.Trim()), DateTime.Parse(txtEnd.Text.Trim()));
                if ( dt1.Rows.Count >0 )                {
                    foreach(DataColumn col1 in dt1.Columns)                    {
                        col1.ReadOnly = false;                    }
                                    }
                foreach ( DataRow row1 in dt1.Rows)                {
                    DataTable dtQuote1 = new DataTable();
                    dtQuote1.Clear();
                    DataTable dtAuthdetails1 = new DataTable();
                    dtAuthdetails1.Clear();
                    dtQuote1 = AuthWorkdone.View_AuthorsationReport_WorkDone7(row1["Internal Reference"].ToString());
                    if (dtQuote1.Rows.Count > 0)                    {
                        row1.SetField("Quote Amount", Decimal.Parse(AuthWorkdone.View_AuthorsationReport_WorkDone8(row1["Internal Reference"].ToString(),
                                                                                                     dtQuote1.Rows[0][0].ToString()).Rows[0][0].ToString()));
                        dtAuthdetails1 = AuthWorkdone.View_AuthorsationReport_WorkDone9(row1["Internal Reference"].ToString(), dtQuote1.Rows[0][0].ToString());
                        if (dtAuthdetails1.Rows.Count > 0)
                        {
                            if (dtAuthdetails1.Rows[0][3].ToString().Equals("T.B.A"))
                            {
                                row1.SetField("Excess", "T.B.A");
                                row1.SetField("Authorisation Date",DateTime.Parse(dtAuthdetails1.Rows[0][0].ToString()));
                                row1.SetField("Authorisation Amount", Decimal.Parse(dtAuthdetails1.Rows[0][1].ToString()));
                            }

the cloumn "Excess" in the table is varchar 

i am getting the following error on this line of code

Cannot set column 'Excess'. The value violates the MaxLength limit of this column.

row1.SetField("Excess",dtAuthdetails1.Rows[0][3].ToString().ToString());

please can you help the columns has numbers like 0.00 or 500.00 and also words like TBA and ect