I'm running Ubuntu 13.04 64b.

sudo apt-get update works fine, but when I run sudo apt-get upgrade I get these errors:

    Err http://archive.ubuntu.com/ubuntu/ raring-updates/main python3.3-minimal amd64 3.3.1-1ubuntu5.2
      403  Forbidden
    Err http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu/ raring/main gimp amd64 2.8.6-0raring1~ppa
      403  Forbidden
    Err http://archive.ubuntu.com/ubuntu/ raring-security/main python3.3-minimal amd64 3.3.1-1ubuntu5.2
      403  Forbidden
    Err http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu/ raring/main gimp-help-en all 1:2.8-0raring16~ppa
      403  Forbidden
    Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/p/python3.3/python3.3-minimal_3.3.1-1ubuntu5.2_amd64.deb  403  Forbidden
    Failed to fetch http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu/pool/main/g/gimp/gimp_2.8.6-0raring1~ppa_amd64.deb  403  Forbidden
    Failed to fetch http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu/pool/main/g/gimp-help/gimp-help-en_2.8-0raring16~ppa_all.deb  403  Forbidden
    E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Running sudo apt-get upgrade --fix-missing installs some updates, but the above errors still persist when I run apt-get upgrade again.

The software update app shows the error: https://www.dropbox.com/s/2cr450557hmahzz/software_update.jpg and selecting continue shows: https://www.dropbox.com/s/l7u32sxyfbxxeeg/soft_upd2.jpg (sorry for the links, I don't have enough rep to post images)

I am behind a proxy, but apt-get update and web browsing work without issues. I also do not believe a server being down is causing this, as the problem has been there over a month.

Any ideas on how to fix this?