appending row in excel2007,c#

[rajeswari02]

hi,
i need to open already existing excel file(.xlsx format),and add a row by collecting data from textboxes . am using code following. but am getting error at opening file:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using Excel=Microsoft.Office.Interop.Excel;

namespace Hand_Held_Data_Transporter
{
    public partial class AddAccount : Form
    {


        private static Microsoft.Office.Interop.Excel.Workbook mWorkBook;
        private static Microsoft.Office.Interop.Excel.Sheets mWorkSheets;
        private static Microsoft.Office.Interop.Excel.Worksheet mWSheet1;
        private static Microsoft.Office.Interop.Excel.Application oXL;
        object Missing = System.Reflection.Missing.Value;

        public AddAccount()
        {
            InitializeComponent();
        }

      
        private void btnsave_Click(object sender, EventArgs e)
        {

            oXL = new Microsoft.Office.Interop.Excel.Application();
            oXL.Visible = true;
           oXL.DisplayAlerts = true;
            //error on this line
            mWorkBook = oXL.Workbooks.Open(txtbrowse.Text, 0, false, 5, "", "", false, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "", true, false, 0, true, false, false);
           // mWorkBook = oXL.Workbooks.Open(txtbrowse.Text);
 
            //Get all the sheets in the workbook
            mWorkSheets = mWorkBook.Worksheets;

            //Get the allready exists sheet
            mWSheet1 = (Microsoft.Office.Interop.Excel.Worksheet)mWorkSheets.get_Item("Sheet1");

            Microsoft.Office.Interop.Excel.Range range = mWSheet1.UsedRange;

            int colCount = range.Columns.Count;
            int rowCount = range.Rows.Count;

            //for (int index = 1; index < 15; index++)
            //{
            mWSheet1.Cells[rowCount + 1, 1] = txtid.Text;
            mWSheet1.Cells[rowCount + 1, 2] = txtname.Text;
            mWSheet1.Cells[rowCount + 1, 3] = txtplace.Text;
            mWSheet1.Cells[rowCount + 1, 8] = txtdue.Text;

            //}
            
            mWorkBook.SaveAs(txtbrowse.Text, Microsoft.Office.Interop.Excel.XlFileFormat.xlWorkbookNormal,
            Missing, Missing, Missing, Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive,
            Missing, Missing, Missing,
            Missing, Missing);

            //mWorkBook.Close(Missing, Missing, Missing);
           // mWSheet1 = null;

           // mWorkBook = null;

            //oXL.Quit();
            GC.WaitForPendingFinalizers();
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
}
        

        private void btnbrowse_Click(object sender, EventArgs e)
        {
            OpenFileDialog fdlg = new OpenFileDialog();
            fdlg.Filter = "All Files(*.*)|*.*";
            if (fdlg.ShowDialog() == DialogResult.OK)
            {
                txtbrowse.Text = fdlg.FileName;
                File.ReadAllText(txtbrowse.Text);

            }
        }

     
       
       
    }
}