The problem with my above code (if I am not wrong) is that
1) I have used two modules - WWW::Mechanize and HTTP::Request.
2) I have set the cookie with the HTTP::Request module and downloaded the web page by the Mechanize object.
It is for this reason that my downloaded page was showing "Your session has expired."

I have made some changes to my program but still the problem persists.(session expired)
The complete changed program is as below.

#!/usr/bin/perl
# Stats.plx

use warnings;
use strict;
use WWW::Mechanize;
use File::Basename;
use DBI;
use Date::Manip;
use Template::Extract;
use Data::Dumper;

my $agent;

$agent = WWW::Mechanize->new( autocheck => 1 );

$agent->get("http://www.abc.com/ChooseZone.aspx?type=A");

print "Making HTTP Post Request....\n";

$agent->get("http://www.abc.com/ChooseZone.aspx?type=A &__EVENTTARGET=
+rdlZone_0 &__EVENTARGUMENT= &__VIEWSTATE='dDw0NzUyOTE0NzQ7dDw7bDxpPDE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' &rdlZone = 1");

$agent->get("http://www.abc.com/CalendarDisp.aspx",":content_file" => 
+"cal.html" );
[download]

Please suggest, esteemed monks!!