Timeout expired error after adding download file code

[bonita]

If I add the code for user to download the file (e.g.
if(File.Exists( FILE_NAME)){... ...}), the ASP.NET will give the
following timeout error:

Timeout expired. The timeout period elapsed prior to completion of the
operation or the server is not responding.

It seems that the download file code is executing before letting the
previous code to finish. Even the message print code
(message.Text=" ...";) is not executed.

What could I do to eliminate this problem. These are the codes for my
ASP.NET application.

private void run_Click(objec t sender, System.EventArg s e)
{
message.Text="" ;
bool alert=false;
string connectionStrin g =
ConfigurationSe ttings.AppSetti ngs["connString "];
SqlConnection connection = new SqlConnection(c onnectionString );
if(option.Selec tedValue.ToStri ng()=="C")
{
SqlCommand command = new
SqlCommand("inl etter3_uterm",c onnection);
command.Connect ion=connection;
command.Command Type=CommandTyp e.StoredProcedu re;
command.Command Text = "inletter3_uter m";
.........
connection.Open ();
command.Execute NonQuery();
connection.Clos e();
string commandString ="select
rtrim(ref)+'/CEM/Rfd/'+rtrim(user_de pt_no)+'/'+substring(con vert(char,sel_d ate,112),3,4)
as ref_val,"+
"rtrim(convert( char,DATENAME(m onth, iss_date)))+'
'+rtrim(convert (char,day(iss_d ate)))+',
'+rtrim(convert (char,year(iss_ date))) as iss_date,"+
"rtrim(D.ti tle) as title from iv_letter3 L, iv_dept D where
L.user_dept_no = D.dept_no";

SqlDataAdapter dataAdapter = new SqlDataAdapter( commandString,
connectionStrin g);
DataSet ds = new DataSet();
dataAdapter.Fil l(ds);
DataTable dt = ds.Tables[0];

string FILE_NAME=@"c:\ inventry\doc\in let3ut.txt";
StreamWriter sw = new StreamWriter(FI LE_NAME, false,
System.Text.Enc oding.ASCII);
foreach (DataRow dataRow in dt.Rows)
{
sw.WriteLine("# "+dataRow["ref_val"].ToString().Tri m());
sw.WriteLine(da taRow["iss_date"].ToString().Tri m());
sw.WriteLine(da taRow["title"].ToString().Tri m());
}
sw.WriteLine("# ");
sw.Close();

if(updatedate.C hecked==true)
{
SqlCommand command2 = new
SqlCommand("inu tmti_upd",conne ction);
command2.Connec tion=connection ;
command2.Comman dType=CommandTy pe.StoredProced ure;
command2.Comman dText = "inutmti_up d";
............... ..
connection.Open ();
command2.Execut eNonQuery();
connection.Clos e();
}
message.Text="U ser Termination/Obsolete Letter successful
printed to a file\n";
//if such codes are commented, there is not timeout expired
error
if(File.Exists( FILE_NAME))
{
FileInfo myFileInfo = new FileInfo(FILE_N AME);
String filename = Path.GetFileNam e(FILE_NAME);
Response.Clear( );
Response.Conten tType = "applicatio n/octet-stream";
Response.AddHea der("Content-Disposition","a ttachment;
filename=\"" + filename + "\"");
Response.AddHea der("Content-Length",
myFileInfo.Leng th.ToString());
Response.Flush( );
Response.WriteF ile(FILE_NAME);
Response.End();
Response.Close( );
}
//end of codes giving timeout expired error
}
}