Got same issue. Cause : my old account of calendar was declared as default calendar in settings, applications, calendar. I think it's a bug.
I found 2 workarounds on this forum. Some delete the /home/user/.calendar/db file. Others edit this db file with a SQLite browser for deleting corrupted entries. I choose the second option and it worked for me. I used devel-su plus develsh for managing this very well hidden file.