Well, that was odd. Managed to get WebCal ( http://wiki.davical.org/w/DAViCal_Web_Client_Installation ) to work (after realising it doesn't hook into the DAViCal database at all - it's a completely separate admin account, user accounts etc). After creating user, couldn't add calendars to them. Eventually tracked it down to utils/helper.php and the encode and decode functions which were retrieving $iv of the wrong lengths - saw 21 and 24 bytes. After putting code in to watch the variables created a new user - which worked perfectly. Disabled debugging code, deleted all users and recreated Glasgow10m user - works fine. Bizarre.