The issue stems from Task diary error that could have been done when creating the affected user.
Note: If you or your system administrator don't have access to User Profiles, please raise a new case online and reference the title of this article.
To fix follow the steps below:
Enter User Profiles.
Go to Task Diary.
Make a change for each of the four points (either select or deselect a user, something easy so you can quickly change back afterward).
Click save.
Have the user log in.
Confirm there are no more errors for the user, then switch back to the settings that were before in User Profiles.