I have the above code for creating the table using interop c#. while calling the same function "FillWordPaPer" ,it gives the error " Cannot access individual columns in this collection because the table has mixed cell widths"

public void FillWordPaPer(List<DTO> DTOList, CustomMainDTO DTO, 
  Document document, int level
    {
        int currentSubLevel = level
        if (currentSubLevel > 0)
        {
            if (!string.IsNullOrEmpty(DTO.Description))
            {     
                int appendingIndex = 0;
                    string appendingtext = string.Empty;
                    for (int i = 0; i < currentSubLevel; i++)
                    {
                         appendingtext = appendingtext + "\r\n";
                    }
                    object oEndOfDoc1 = "\\endofdoc";
                    Microsoft.Office.Interop.Word.Table testTable;
                    Microsoft.Office.Interop.Word.Range wrdRng1 = document.Bookmarks.get_Item(ref oEndOfDoc1).Range;
                    testTable = document.Tables.Add(wrdRng1, 1, 2, ref missing, ref missing);
                    testTable.Columns[1].SetWidth(20, WdRulerStyle.wdAdjustSameWidth);
                    testTable.Columns[2].SetWidth(400, WdRulerStyle.wdAdjustSameWidth); 
                    testTable.Cell(1, 1).Range.Text = appendingtext;                       
                    testTable.Cell(1, 2).Range.Text =DTO.Title;
            }
        }
        var subData = nDTOList.Where(q => q.ParentID == DTO.ID);
        sublevel++;
        foreach (var item in subData )
        {
            if (!insertedIds.Any(x => x == item.ID))
            {
                insertedIds.Add(item.ID);

                FillWordPaPer(DTOList, item, document, sublevel);
            }
        }
  }