Excel Import Error in ASP.net

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C#

ASP.NET

MS-Excel

I am trying to import an excel to databse from asp.net website through dataset.
here is my first part.

int xlColCount = 1;
       wb = app.Workbooks.Open(FilePath, 0, false, 5, "", "", true, Ex.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);
       ws = (Ex.Worksheet)wb.ActiveSheet;
       xlColCount = ws.Columns.Count;
       xlColCount = ws.UsedRange.Columns.Count;


       ws.Columns.ClearFormats();

       xlColCount = ws.UsedRange.Columns.Count;

       //creating datacolumns
                   for (int i = 0; i < xlColCount; i++)
                   {

                       try
                       {
                           DSname.Tables[0].Columns.Add(((Ex.Range)ws.Cells[1,strColArr[i]]).Value2.ToString().Trim());
                       }
                       catch(Exception ex)
                       {
                           //error occured
                       }
                   }

first i am creating the column name based on the excel heading into dataset column.here xlColCount=198(total no.of columns from the excel template and all are filled ) but when reaching 172th column(i=172) it is giving index out of range error.

what could be the reason.I need to create a dataset with coulmn names from all excel coulmn names.

Anyone pls help it is urgent....