Error adding new user - pw: user 'qwe' disappeared during update

As root, I'm trying to add a new user with adduser but it returnes a strange error when I confirm. Only the group 'anne' gets created, but nothing more. I checked pw(8) for something helpful as it seems like it's pw creating the error and checked /var/log/messages and /var/log/auth.log but nothing strange there.

Username   : anne
Password   : *****
Full Name  : Anne
Uid        : 2001
Class      :
Groups     : anne
Home       : /home/anne
Home Mode  :
Shell      : /bin/sh
Locked     : no
OK? (yes/no): yes
pw: user 'anne' disappeared during update
adduser: ERROR: There was an error adding user (anne).
Add another user? (yes/no): no
Goodbye!

Anyone who could help? Thanks!

Your databases are out of sync. Not sure how this happens but I get it from time to time too. Run /usr/sbin/pwd_mkdb -p /etc/master.passwd. Running vipw(8) and save-and-quit (without actually making any changes) also fixes it (easier to remember).