> <http://www.forexfactory.com/calendar.php>

There are no links to previous months on the page so HTT gets nothing. 
The buttons in the calendar COULD have been simple links but instead it uses
onclick="window.location = 'calendar.php?c=2&amp;week=...'" making them a type
of form - HTT doesn't click on forms.
The monthly view uses
<http://www.forexfactory.com/calendar.php?month=2&year=2012&fullmonth=1> You can
create a list via HTTrack Help: URL number sequences
for /l %Y in (2012,-1,2007) do for /l %M in (12,-1,1) do echo
<http://www.forexfactory.com/calendar.php?month=%M^&year=%Y^&fullmonth=1>
>>c:\urls.txt