When adding an ical feed to the calendar, user gets an error, "The content of this URL does not
conform to the iCalendar parsing specification."
User gets error when adding an ical feed via calendar federation
The link that is pointing to the ics file is invalid
Diagnosing the problem
Download the ics file associated with the feed to your local machine. You should be able to import the file into Notes just fine.
Placing the ical feed's URL into a browser also fails.
Resolving the problem
In this case, a third party application called TripIt was being used to create the icalendar feed. It was found that the URL generated by TripIt was invalid. For additional assistance with this issue please contact the TripIt vendor for additional assistance.
In another case, the customer upgraded to Internet Explorer 9 which resolved the problem.