I'm newbie here and I've got an error installing applets from Ubuntu Software Center which shows the app's icon in the launcher but it doesn't really install! Internet connection is active but I can't update 'other resources' because it gives me internet connection error after taking a long time loading.
Screenshots:
You can remove the cdrom by undoing the selection you did before in Software & Updates > Other Software.
Also remove the offending file:
sudo rm /etc/apt/apt.conf.d/20auto-upgrades.ucf-dist
Now you should be able to download and install updates and other software.