Please use the LoadOptions class instead of TxtLoadOptions class because the later one is supposed to be used for loading text files such as CSV. Please check the below provided code snippet for better elaboration.
C#
LoadOptions m_tLoadOpt = new LoadOptions(LoadFormat.Excel97To2003);
m_tLoadOpt.ConvertNumericData = false;
Workbook m_Workbook = new Workbook(myDir + “output.xls”, m_tLoadOpt);
Please feel free to write back in case you have any concerns or ambiguity.