Hi!
This error you got: Fatal error: Cannot redeclare class calendar in /home/sites/flog-it.ie/public_html/calendar.cls.php on line 4
Comes because you are including the file calendar.cls.php more then one time. When the Calendar class already exists, you can not include another (or the same) class with this name. I can't find you your code the second place you including this file, so maybe you are inclduing it another place?
What I would advise you to do is look for other places this file is included. But as a quick way to fix this change line 2 in caltest.php
from: include("calendar.cls.php");
to: include_once "calendar.cls.php";
What this does is, is including the file if, and only if it has'nt been included earlier.
As a reminder: when you develop systems as this. Make sure you have control over the files that get included, so errors like this doesnt happend.