For security purposes a user's account will be locked if their password has been entered incorrectly more than five times. If a user becomes locked they will receive the below message directing them to use the "Forgotten Password?" link. Using the Forgotten Password feature will send the user a new password and unlock their account.
Searching for Locked Users
To search for locked users go to Administration module > Users. Click the downwards arrow to show all available filters. You can then change the State filter to Locked and select Search.
Unlocking Users
Community Administrators and User Administrators can also unlock a user's account by editing the user, selecting Unlock.