A user can be locked when he or she filled in the password wrong too many times. An error as seen below in the bottom left corner will appear.
A user account can be unlocked by an admin, owner or operator. It is shown that a user is locked by a lighter grey colour and the letters (locked) behind the name of the user, as can be seen in the image below for a Roy Heller.
To unlock a user, go to a course the user is in, click Users in the menu and find the users name. Click on the three dots on the right side of the bar of the user. In the drop-down menu that appears, the option Unlock account is visible. Click this option and the user's account will be unlocked again. The user can now log in again.