I had this problem in the past with my iPod and suddenly the same is happening to my iPhone: Calendars are no longer syncing to my 'iDevices.' This started with 10.5 for me, but I don't know that it's related to the OS version. There are lots of Apple Discussions suggesting to export all calendars, delete them in iCal, and then re-import them. Resetting the Sync History in iSync's Preferences is also mentioned all the time as a possible solution. I tried those methods, but they never worked for me. Sometimes the calendars list in iTunes just went empty, and other times it didn't show all my calendars or only very old, long-deleted ones. Since the behavior was the same with my iPod and my iPhone, I could at least rule out a problem there. Today I finally discovered the culprit: I am sharing my calendars via icalx.com, and it turns out that sometimes iCal simply "forgets" the URL I have set th...

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