system hangs on shutdown

[e-fernbach]

shutdown hangs with the last line in terminal "will now halt"

the problem seems to be modemmanager and nm, error message: nm-dispatcher.action could not aquire the org.freedesktop.nm_dispatcher service

hardware: Siemens/Nixdorf AmiloPro, Celeron Processor
software: Lubuntu 14.10, Kernel: 3.16.0-28-generic, Gnome 3.12.2

[e-fernbach (e-fernbach)]

purged modemmanager problem persists
shutting down network manager before issuing shutdown command problem persists

messages on screen in the latter case:
wait-for-state stop/waiting [ok]
*stopping uuidd generator uuidd [ok]
* asking all remaining processes to terminate [ok]
* all processes terminated within 1seconds [ok]
*deactivating swap [ok]
will now halt

sounds all very clean and yet no power off

[e-fernbach (e-fernbach)]

booted the system with a live Lubuntu 14.10 32bit DVD and performed a shutdown. The system hangs after asking to remove the DVD.

As a control I did the very same with a Lubuntu 14.04 LTS 32bit DVD. The system shuts down normally. Thus I conclude that the error was introduced with the 14.10 upgrade.