The error comes up with "remember me", after the session has expired.
To reproduce this, set in config/config.php => Session Variables the expriation value to a short time, i.e.
Code:
$config['sess_expiration'] = 10;
Now log in with "remember me", wait some seconds and reload the page several times (up to 6 -10 times). Sometimes the error messages come, sometimes they don't.