This worked for me with Ubuntu 12.04 on an Acer laptop as well.
wired device not managed
I had the same problem with a fresh install on my Asus Eee PC 1005HA. The live environment worked with no problems, but once installed I couldn't get the connection to respond or to not read "device not managed". When I changed the text in this configuration file and restarted Network Manager everything worked!gksudo gedit /etc/NetworkManager/NetworkManager.conffor lubuntu:gksudo leafpad /etc/NetworkManager/NetworkManager.conf
Now the text editor will open. Find the line managed=false and replace false with true and save the file (ctrl+s) and close the file.
Restart your computer or the NetworkManager service (sudo service network-manager restart).
Teaching an Ubuntu laptop to recognize the Ethernet connection
Good advice from Joseph VanPelt