Add Main Calendar Link

While I’m not familiar with the Calendarize It! plugin, I took a look at the linked pages, and the issue seems to be you are using pages (instance of the Page post type) instead of the actual calendar category and said page is not a child of the Calendar page. So, on the actual calendar entries (end up being an instance of a custom post type), Breadcrumb NavXT is able to figure out the hierarchy and adds in the calendar category. But on the page that replaces the calendar category archive, Breadcrumb NavXT has no way to know that the calendar page should be a parent as it is not set as a parent of said page. The easy fix appears to be, in the page editor, change the parent page for each of the calendar category pages to Calendar.