ERROR - The system network services are not compatible with this version

[WilliamColls]

After doing the upgrade from 10.04 to 12.04, and rebooting, I get a message "Waiting for network configuration", and a long pause. Eventually I get a message "Continuing to boot without network services". The machine eventaully comes up to the desktop, and I can select System Settings -> network, and the message is displayed. ifconfig seems to detect the network device correctly. I have no idea where to start with this. Any help will be greatly apprecaited. (it was all working just fine under 10.04)

Thanks for your time.

William.

[SteveRiley]

If you enter

sudo service network-manager start

in a console window, does networking begin functioning normally?