Failed to download repository information due to missing CDROM

When updating I got this error message:

W:Failed to fetch cdrom://Ubuntu 11.10 _Oneiric Ocelot_ - Release amd64 (20111012)/dists/oneiric/main/binary-i386/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
W:Failed to fetch http://ppa.launchpad.net/synce/ubuntu/dists/your_ubuntu_version/main/source/Sources  404  Not Found

What to do?

Solution 1:

Run "Software & Updates" and uncheck checkbox near "Cdrom with Ubuntu"

Solution 2:

The issue here is that your OS is looking for CD-ROM in the apt sources list. To fix this:

sudo vi /etc/apt/sources.list

Remove any lines that include CD-ROM. Save the file and try once more.

Solution 3:

The W: lines are warnings. The first one is because you still have your install CD (the one you used to install Ubuntu in the first place) listed as a possible software source, but it is not in your drive at this time (reasonable, ignore it). The second is because you have copied a URL (web address) verbatim and not changed your_ubuntu_version to the name of your Ubuntu version. It should read http://ppa.launchpad.net/synce/ubuntu/dists/oneiric/main/source/Sources instead, since you're using Oneiric Ocelot (11.10).

You can access Software Sources through the Ubuntu Software Centre to make changes to your source lists - https://help.ubuntu.com/community/Repositories/Ubuntu#Adding_Repositories_in_Ubuntu