Ubuntu 11.10: updates fails... W:Failed to fetch cdrom

Do this:
1. Open a terminal by hitting CTRL + ALT + T
2. Insert and run this command:
cat /etc/apt/sources.list -n

3. Copy and paste here all the terminal output.

run:

gksudo gedit /etc/apt/sources.list

there are the top few lines referencing the CD, add a hash character at the start to make them comments, save the new file and close gedit. A hash character is a '#'

Now when you run:

sudo apt-get update

Is it smooth?

you can do it via the graphicl interface by clicking on software sources, then at the bottom of the window that pops up, uncheck the box opposite CD-ROM

I had the same problem. Advice from #1 and #2 above solved it.
The output after sudo apt-get update WAS smooth and Update Manager

After trying to update via Update Manager would always get the following

Failed to download repository information

W:Failed to fetch cdrom://Ubuntu 11.10 _Oneiric Ocelot_ - Release amd64 (20111012)/dists/oneiric/Release Unable to find expected entry 'restricted/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)

Using the graphical interface to uncheck the box opposite CD-ROM did not work.

Update Manager did manage to install updates. It just never recognised that updates had been achieved.
(last update message was stuck at 1 then 2 then 3 days.

MANY THANKS TO BOTH SUGGESTIONS ABOVE

Thanks ... followed advice from #2. Worked Great.