Asp.net gives error while downloading file "The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write()"

I have a web page and  this contains one button, when user clicks on this button i am calling a fucntion of one of my class.
this function will write a excel file which need to be downloaded.
 ExportDB exportDB = new  ExportDB();
        exportDB.ExportDBToExcel();

After this i am calling this function which exits in my web page itself
        DownloadFile();

When i am runing the code then the excel file is getting created properly but after that when i calll the downloadfile function it exceutes every line after that it gives me this error.

===========================================================================
Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.

Details: Error parsing near 'ÿ<table border="1">'.
===========================================================================

Any one could help me out here.
I am giving the my complete code below.

this is my export db class code
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Text;
 
 
public class ExportDB {
    private DBFunctions _dbFunctions = null;
    private DataSet _dataset = null;
    private HtmlTable _htmlTable = null;
    HtmlTableRow _tableRow = null;
 
	public ExportDB() {
	}
 
    private void PrepareMCHTMLTable() {
        _htmlTable = new HtmlTable();
        _htmlTable.Border = 1;
        _tableRow = GetMCHTMLTableRow();
 
        _tableRow.Cells[0].InnerHtml = "<b>SNo.</b>";
        _tableRow.Cells[1].InnerHtml = "<b>Source</b>";        
        _tableRow.Cells[2].InnerHtml = "<b>ID</b>";
        _tableRow.Cells[3].InnerHtml = "<b>Title</b>";
        _tableRow.Cells[4].InnerHtml = "<b>TRANS_CODE</b>";
        _tableRow.Cells[5].InnerHtml = "<b>MIGRATED</b>";
        _tableRow.Cells[6].InnerHtml = "<b>Parent</b>";
        _tableRow.Cells[7].InnerHtml = "<b>Child</b>";
        _tableRow.Cells[8].InnerHtml = "<b>Issue</b>";
        _tableRow.BgColor = "#D4D0C8"; 
        _htmlTable.Rows.Add(_tableRow);        
    }
 
 
    private HtmlTableRow GetMCHTMLTableRow() {
        HtmlTableCell tableCellMC = null;
        HtmlTableCell tableCellOID = null;
        HtmlTableCell tableCellID = null;
        HtmlTableCell tableCellTitle = null;
        HtmlTableCell tableCellTransCode = null;
        HtmlTableCell tableCellMigrated = null;
        HtmlTableCell tableCellTopicParent = null;
        HtmlTableCell tableCellTopicChild = null;
        HtmlTableCell tableCellTopicIssue = null;
        HtmlTableRow _tableRow = null;
        
        tableCellMC = new HtmlTableCell();
        tableCellMC.Width = "90";
        tableCellMC.InnerText = "MC (Mobile)";
        tableCellOID = new HtmlTableCell();
        tableCellOID.Width = "50";
        tableCellID = new HtmlTableCell();
        tableCellID.Width = "100";
        tableCellTitle = new HtmlTableCell();
        tableCellTitle.Width = "300";
        tableCellTransCode = new HtmlTableCell();
        tableCellTransCode.Width = "100";
        tableCellMigrated = new HtmlTableCell();
        tableCellMigrated.Width = "100";
        tableCellTopicParent = new HtmlTableCell();
        tableCellTopicParent.Width = "150";
        tableCellTopicChild = new HtmlTableCell();
        tableCellTopicChild.Width = "150";
        tableCellTopicIssue = new HtmlTableCell();
        tableCellTopicIssue.Width = "300";
 
        
 
        _tableRow = new HtmlTableRow();        
        _tableRow.Cells.Add(tableCellOID);
        _tableRow.Cells.Add(tableCellMC);
        _tableRow.Cells.Add(tableCellID);
        _tableRow.Cells.Add(tableCellTitle);
        _tableRow.Cells.Add(tableCellTransCode);
        _tableRow.Cells.Add(tableCellMigrated);
        _tableRow.Cells.Add(tableCellTopicParent);
        _tableRow.Cells.Add(tableCellTopicChild);
        _tableRow.Cells.Add(tableCellTopicIssue);        
 
        return _tableRow;
    }
 
    public void ExportDBToExcel() {
        int counter = 0;
        
        DataRow[] selectedDataRow = null;
        DataRow rowParent = null;
 
        _dbFunctions = new DBFunctions();
        if (_dataset == null) { _dataset = new DataSet(); }
        _dbFunctions.GetMCFAQ(_dataset);
        if (_dataset.Tables["Topic"].Rows.Count > 0) { PrepareMCHTMLTable(); }
 
        foreach (DataRow row in _dataset.Tables["Topic"].Rows) {
            _tableRow = GetMCHTMLTableRow();
            counter += 1;
 
            _tableRow.Cells[0].InnerText = counter.ToString();
            if (row["QuestionPkey"] == DBNull.Value) {
                _tableRow.Cells[2].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[2].InnerText = row["QuestionPkey"].ToString();
            }
 
            if (row["Title"] == DBNull.Value) {
                _tableRow.Cells[3].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[3].InnerText = row["Title"].ToString();
            }
 
            if (row["TRANS_CODE"] == DBNull.Value) {
                _tableRow.Cells[4].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[4].InnerText = row["TRANS_CODE"].ToString();
            }
 
            if (row["Migrated"] == DBNull.Value) {
                _tableRow.Cells[5].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[5].InnerText = row["Migrated"].ToString();
            }
                        
            if (row["ParentPKey"] == DBNull.Value) {
                _tableRow.Cells[6].InnerHtml = "&nbsp";
            } else { 
                selectedDataRow = _dataset.Tables["TopicParent"].Select("Pkey=" + row["ParentPKey"].ToString());
                if (selectedDataRow.Length > 0) {
                    rowParent = selectedDataRow[0];
                    _tableRow.Cells[6].InnerText = rowParent["TopicName"].ToString();
                } else {
                    _tableRow.Cells[6].InnerHtml = "&nbsp";
                }
            }
 
            if (row["TopicName"] == DBNull.Value) {
                _tableRow.Cells[7].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[7].InnerText = row["TopicName"].ToString();
            }
 
            if (row["IssueName"] == DBNull.Value) {
                _tableRow.Cells[8].InnerHtml = "&nbsp";
            } else {
                _tableRow.Cells[8].InnerText = row["IssueName"].ToString();
 
            }
 
            _htmlTable.Rows.Add(_tableRow);
        
        }
 
        PrepareExcelFile();
 
    }
 
    private void PrepareExcelFile() {
        if (_htmlTable == null) { return; }
        StringWriter tw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(tw);
        _htmlTable.RenderControl(hw);
        string HtmlInfo = tw.ToString().Trim();        
        string DocFileName = "ExportDB.xls";
        string FilePathName = HttpContext.Current.Server.MapPath("Images/ExportDB.xls");        
                
        File.Delete(FilePathName);
        FileStream Fs = new FileStream(FilePathName, FileMode.Create);
        BinaryWriter BWriter = new BinaryWriter(Fs, Encoding.GetEncoding("UTF-8"));
 
        BWriter.Write(HtmlInfo);
        BWriter.Close();
        Fs.Close();
        
        tw = null;
        hw = null;
        Fs = null;
        BWriter = null; 
 
    }
 
    
}
 
 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
This is my download file code.
 
 private void DownloadFile() {
        string fileName = "ExportDB.xls";
        string filePathName = HttpContext.Current.Server.MapPath("Images/ExportDB.xls");
        FileStream liveStream = new FileStream(filePathName, FileMode.Open,
                                       FileAccess.Read);
 
        byte[] buffer = new byte[(int)liveStream.Length];
        liveStream.Read(buffer, 0, (int)liveStream.Length);
        liveStream.Close();
 
        Response.Clear();
        Response.ContentType = "application/octet-stream";
        Response.AddHeader("Content-Length", buffer.Length.ToString());
        Response.AddHeader("Content-Disposition", "attachment; filename=" +
                           fileName);
        Response.BinaryWrite(buffer);
        Response.End();
 
    }

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