1) Reboot the switch
2) Default the user name and password from engineering mode.
Note: Defaulting the password from engineering menu require additional information, contact support for further assistance.
4850GTS(config)#password aging-time ? <1-365> Number of days username Set the aging-time for a specified userEven if the password security is disabled in ERS 4800/4900/5900, the issue can manifest based on the password aging timer configured on the switch this value varies from 1-365 days for the switch running version 5.8.0.x for ERS 4800 and 7.0.0.x for ERS 4900/5900.