This icon means that your user has been blocked
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This happens because you entered your password incorrectly too many times. The blocking of the user will typically occur after 3-5 incorrect login attempts.
How to unlock a blocked user
To unlock a blocked user, the password must be changed. Only the user can do that. Click the "Forgot Password?" link at the bottom of the page - either on the web or in the app and follow the instructions for forgotten password.