I'm also having this problem, specifically I'm trying to import an .ics file from iCal v2.0 on my old PB G4 (yes, I was overdue for an update!)
Its not just a Mavericks problem because I'm using Mountain Lion 10.8.5 and its not just a question of switching to the calendar.app (see mrabne's post) because that also doesn't work for me.
This isn't an iCloud problem for me as I don't use that, nor do I receive .ics files from others. I'm just trying to transfer my old information to my new computer!
Interestingly enough, its such a basic inherent problem that when I export the (empty) Work calendar from Calendar v6 and then try to reimport it right back into the same program, it says it can't read that .ics file either!
I can't find any .ics files but the one for Timezone so I don't think that's the issue.
I'm no crack, just a normal user. What am I missing? What can I try doing to solve this?
This is very frustrating. After all this money spent on a new macbook, you would think my loyalty would be rewarded with some continuity and the ability to transfer such basic information as a calendar into a newer version of the very same program. This is one of the many issues I've had as I haven't been able to simply migrate because Tiger is already too old to bother making compatible even for a migration. Apple's lesson: Keep buying new (buggy) products and feeding the money machine or you'll be permanently cut off!