I downloaded & installed the EventCalendar module, and after working out that the folder name had to be changed for the install to work I managed this without a problem.
1) The date links from a calendar don't always work. This can be seen on the demo site: http://eventcalendar.bluehousegroup.com/new-calendarevent-4/ click on a date link on the calendar on this page, and you go to : http://eventcalendar.bluehousegroup.com//2010-01-06 , which gives you an error of some kind.
2) After installing the SiteTree in the admin area stopped working properly. Every time I clicked a page in the SiteTree I got a spinning icon in the tree for probably five minutes before the page appeared. When I removed eventcalendar & rebuilt the database this issue went away. Put the eventcalendar back, issue comes back. No other changes were made, so there is no doubt that the eventcalendar is causing this. There are no errors in the site's error log either, so I have no idea what the problem might be.
Thanks in advance.