Redmine

Hi, trying to get ics/icalendar data from redmine to integrate with outlook..
I have installed icalendar
Not sure how to get ICS data.. seen a forum entry that suggests
http://########/redmine/projects/calendar/PROJECTNAME?format=ics

This returns 403 You are not authorized to access this page.

Can anyone shed some light on how to get at the ical data

Ta