Default Calendar sync problems

I'm getting this msg every time I'm trying to add new event to the calendar:
"Local calendar cannot sync with Google calendar. You need a Google account"
I can of course choose to never see it again, but still there have to be a reason why it is displayed.
Syncing events with main calendar works without any problems, both ways. Only sync problems I'm getting are with external (read-only) calendars. I can see them on calendar list, but they do not appear in calendar itself (most of the time, they sometimes appear for few hours).