Root locked out on freeBsd. After managing user accounts with kUser various users accounts may become expired, including
root. Attempts to login as root are confronted with this error:
pam_acct_mgmt(): user accound has expired
login incorrect
# chfn root
  Reveals that root account expires in 1969. 
Resolution:
  Reboot then choose command line option or escape to loader prompt during boot count sequence.
  
  # unload all
  # load kernel
  
  # boot -s
  ***singleUserMode-*
  Hit enter at shell prompt
  
  # mount -t ufs -a
***readWriteMounts fileSystems derived from etc/fstab-*
  # vipw
  ***opens the password file with vi-*
  Edit the userExpirationFlags from   :-1:   to   :0:   and save.
  
  # passwd root
  # pwd_mkdb /etc/master.passwd
  
 # exit
***returns to multiUserMode-*
Login then REBOOT!
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***You could also try this:-*
If your bios supports rolling back to a date before 1969, you might give that a try first!