[Mailman-Users] mailman upgrade failing

[Noah]

Hi there,

Mailman upgrade keeps failing on my ubuntu server and not clear why? 
qrunner hangs every week so upgrading might be the right thing to do.

Preparing to replace mailman 1:2.1.9-9ubuntu1.2 (using 
.../mailman_1%3a2.1.9-9ubuntu1.4_amd64.deb) ...
  * Stopping Mailman master qrunner mailmanctl          No child with 
pid: 11139
[Errno 3] No such process
Stale pid file removed.

   [ OK ]
dpkg: error processing 
/var/cache/apt/archives/mailman_1%3a2.1.9-9ubuntu1.4_amd64.deb (--unpack):
  subprocess pre-installation script returned error exit status 1
No updates are necessary.

Any clues what I can do to get apt-get upgrade to work?

Cheers,
Noah