While apt-get upgrade-ing a server that apparently had bind9 installed, it barfed out complaining about something about sendmail. Weird, as sendmail isn’t installed (at least not any longer), but since sendmail isn’t installed, it couldn’t be removed either.
The solution: mv /etc/resolvconf/update-libc.d/sendmail /tmp — and run dpkg / apt-get / aptitude again. If it works now (and you don’t have sendmail installed either), delete the file from /tmp.
/etc/resolvconf/update-libc.d/sendmail: 7: .: Can't open /usr/share/sendmail/dynamic run-parts: /etc/resolvconf/update-libc.d/sendmail exited with return code 2 run-parts: /etc/resolvconf/update.d/libc exited with return code 1 invoke-rc.d: initscript bind9, action "restart" failed. dpkg: error processing bind9 (--configure): subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing: bind9