Hi jchiar,
The iCalendar Events feed is an iCalendar feed that treats your tasks as calendar events based on their due date. Each of your lists has an iCalendar Events feed, but the "All Lists" feed, found on the Info tab, includes all tasks from all lists. This is an authenticated feed which will require your username and password to subscribe to it.

Google Calendar does not currently support authenticated feeds. However, you should be able to subscribe using iCal. This page gives instructions under the "Showing tasks on the calendar in iCal" heading.

If you're having trouble subscribing, would you be able to contact us so we can take a closer look?

Thanks!