Weird problem. Using Calendar in Mountain Lion, and I have 6 shared iCloud calendars and one "On My Mac" calendar. All the calendars show up, and I can tick and untick them as I like. However, on this Mac, if I try to add a new event, the only calendars I can add them to are the "On My Mac" calendar, and two of the six shared iCloud calendars. If I use my other Mac (same iCloud account), I can add events to whatever calendars I like. I can't find any particular permission settings or sharing options - anyone have any idea? Not being able to add events to the calendars on this desktop machine (the primary Mac in the house) is a major problem.