Hi,
There is a little bug in the 0.60 beta version in the file named admin/categories.php at the line 283 :
<a href='$mod_url?action=Edit&cid=$cid' target='_blank'><img src='$cal->images_url/addevent.gif' border='0' width='14' height='12' /></a>
$mod_url only contains the path to the module.