For some reason, whenever I try to search for updates with Ubuntu 12.10's update manager, I always get this error: Failed to download repository information, followed by the following details:

W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/Release.gpg Unable to connect to extras.ubuntu.com:http:

, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/i18n/Translation-en Unable to connect to extras.ubuntu.com:http:

, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/i18n/Translation-en_CA Unable to connect to extras.ubuntu.com:http:

, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/source/Sources Unable to connect to extras.ubuntu.com:http:

, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/binary-amd64/Packages Unable to connect to extras.ubuntu.com:http:

, W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/main/binary-i386/Packages Unable to connect to extras.ubuntu.com:http:

, E:Some index files failed to download. They have been ignored, or old ones used instead.

Initially I thought that for whatever reason the repositories were down, so I switched from the Canada server to the main server. I still got the same error. I also tried installing some things from the ubuntu software center. Funny thing is, that worked fine and I was able to successfully download and install software from the software center, so it seems that only update manager can't access the repositories.

I have searched for and found similar cases (relating to ubuntu 12.10), but most of those cases involved ppa's, and I don't use any ppa's.

Help would be appreciated. Thanks.