Unable to update excel (.xls) file in WCF deployed on Windows server 2008 R2

This issue is specific to a case, when i am trying to update an existing excel file via WCF. Please note that i am able to read excel files and the issue only occurs when i try to update any excel file. Also, this update logic works perfectly fine on my development environment (WinXP where as production environment is Windows server 2008 R2).

I have tried the steps mentioned in Borgon's Blog (http://hopschwiiz.blogspot.com/2011/02/automating-excel-2007-on-windows-server.html) as well but without any luck.

I am using .Net 3.5, SQL Server 2008 & SL 3.0.

As requested have added the codes...

string[] strArray;
string fileName = null;
System.Array myvalues = null;
Microsoft.Office.Interop.Excel.Application ExcelObj = null;

try
{
    fileName = System.Configuration.ConfigurationManager.AppSettings["FileLocation"].ToString();
    fileName += "JobDetails.xls";

    ExcelObj = new Microsoft.Office.Interop.Excel.Application();
    Excel.Workbook theWorkbook = (Excel.Workbook)ExcelObj.Workbooks.Open(fi开发者_Python百科leName, 0, false, 5, "", "", true, Excel.XlPlatform.xlWindows, "", true, false, 0, false, true, false);
    Excel.Sheets sheets = theWorkbook.Worksheets;
    for (int sheetNum = 1; sheetNum <= sheets.Count; sheetNum++)
    {
        Excel.Worksheet worksheet = (Excel.Worksheet)sheets.get_Item(sheetNum);

        for (int i = 8; i <= 50; i++)
            {
                Excel.Range range = worksheet.get_Range("A" + i.ToString(), "AI" + i.ToString());
                myvalues = (System.Array)range.Cells.get_Value(Type.Missing);
                strArray = ConvertToStringArray(myvalues);

                if (strArray[1].Equals("PSA Id") && strArray[2].Equals("Member Name") && strArray[3].Equals("Project Name"))
                {
                    int j = i;
                    worksheet.Cells[j, 5] = Month; // Updated Month in the excel file.
                    foreach (MemberShift item in listOfJobPlan)
                    {
                        j++;
                        worksheet.Cells[j, 2] = item.MemberID.ToString("D" + 6);
                        worksheet.Cells[j, 3] = item.MemberName;
                        worksheet.Cells[j, 4] = inGroupName;
                    }
                    break;
                }
            }
    }
}
catch (Exception ex)
{
    string Log = "DataService";
    if ((!(EventLog.SourceExists(Log))))
        EventLog.CreateEventSource(Log, Log);
    EventLog logEntry = new EventLog();
    logEntry.Source = Log;
    logEntry.WriteEntry("Message : " + ex.Message + "\n StackTrace : " + ex.StackTrace, EventLogEntryType.Error);
    return false;
}
finally
{
    ExcelObj.Workbooks.Close();
}

return true;

Check to see what user the Website is running as and then make sure that user has the appropriate permissions to edit the files.