No calendar is defined as the default. Whichever calendar that is selected in the left pane of the calendar tab is the one that accepted invitations will be added to.

Unfortunately it don't work. I select the calendar I want to use, put it on top of the list. But when I accept an invitation it still ends up in the home. If I remove the home, it can not save it at all.

Is there something I'm missing?

Best regards /Mike

OK, I've done some tests, and the matter of which calendar is selected is not important for accepting invitations. It does determine which calendar a new event is added to, but not for invitations.

It appears that if an invitation is received in account X, accepting it will add it to the calendar which has account X as the Email specified in calendar Properties. If the invitation is received in an account which is not associated with a calendar, you are prompted to select the calendar to which it will be added.

I suggest you review the calendars to see which Emails they have, and to try and give your gmail address to senders of (most) invitations.