package postfix 2.9.1-5 failed to install/upgrade: ErrorMessage: subprocess installed post-installation script returned error exit status 1

From log:

Setting up postfix (2.9.1-5) ...
Installing new version of config file /etc/init.d/postfix ...
Installing new version of config file /etc/postfix/post-install ...
Installing new version of config file /etc/postfix/postfix-files ...
Installing new version of config file /etc/ufw/applications.d/postfix ...
Installing new version of config file /etc/resolvconf/update-libc.d/postfix ...
Lege Gruppe »postfix« (GID 132) an ...
groupadd: /etc/gshadow konnte nicht gesperrt werden; versuchen Sie es später noch einmal.
addgroup: »/usr/sbin/groupadd -g 132 postfix« gab den Fehlercode 10 zurück. Programmende.
dpkg: error processing postfix (--configure):
 subprocess installed post-installation script returned error exit status 1

"/etc/gshadow could not be locked, try again later."

Thank you for taking the time to report this bug and helping to make Ubuntu better.

This looks like a local configuration problem, rather than a bug in Ubuntu. As such, I'm marking this bug as Invalid.

You can find pointers to get help for this sort of problem here: http://www.ubuntu.com/support/community

If you have a /etc/gshadow.lock file, this is a spurious lock file perhaps left over from an unexpected system power failure or reset and deleting this file could help.

If you believe that this is really a bug, then you may find it helpful to read "How to report bugs effectively" http://www.chiark.greenend.org.uk/~sgtatham/bugs.html. We'd be grateful if you would then provide a more complete description of the problem, and then change the bug status back to New.

Thanks!