Apple iCalendar subscription servers appear to be offline. The servers host iCalendar files which any user with an application that supports the iCalendar (ICS) standard can subscribe to.
iCalendar files can be used in popular apps like Calendar on iOS and OS X and Google Calendars. Subscribable calendars are an easy way for people to add a mass amount of data — like holidays or sporting team events — to their planners. Once subscribed, the calendars automatically update when any changes are made on the server side.
The author of the TUAW piece reports that for the last dew days he noticed that calendars he subscribed to were showing a refresh error icon. Manually refreshing gave an error-1 dialog.
I tried importing the Holidays calendar into my Calendar app and received an error also.
Apple links many calendar subscriptions on its iCal Calendars site. The only ones that seem to be affected are the subscriptions hosted on Apple’s own calendar servers (those beginning with: webcal://ical.mac.com/ical/xxxx.ics).
Apple hasn’t commented on the servers being offline.
If you are currently subscribed to Apple-served iCalendars, you will still see events in your Calendar apps since the last time it was refreshed. If you delete the subscription, with Apple’s iCalendar server currently offline, there will be no way to get the entries back.