In Carerix, tasks aren't visible in the calendar. This page describes an alternative way for showing a task in the calendar.
Change a task into a meeting, as follows:
Click in the left menu on 'Tasks'
Click the button [New] to create a new Task.
In the dropdown menu behind the word 'Kind', select 'Meeting'
Click [Finish] to save the task.
The new task is now visible in your calendar.