iCal/iCloud calendar refuses to import CalDAV event

I'm trying to add a CalDAV event/file to my iCloud calendar in iCal on OSX, but get an error message as shown in the link (in Norwegian): https://www.evernote.com/shard/s68/sh/56aeb0f3-07b1-4a92-8d43-e70ff31498a0/8e777 ad8c51e1b2f0f814ea7f531eac1

Basically it translates into something like: "Host error. Access to the event in "Inbox" in the "iCloud" account is not allowed.

Anyone who can help me solve this problem?

Thanks,

Eivind