These problems only solution is contacting the PPA maintainer, by mail or IRC. It depends the details the owner provided. You can find the contact information clicking the link:
For questions and bugs with software in this PPA please contact Owner link.
There you should click the link:
and explain the problem you are having. Now let me explain why each of them happens.
Err http://ppa.launchpad.net codename/main amd64 Packages
404 Not Found
Err http://ppa.launchpad.net codename/main i386 Packages
404 Not Found
The PPA doesn't have packages available for your repository. The package maintainer has to upload some so Launchpad creates the repository. You can try to use older/newer repository but that's own your own risk. Contact the maintainer and ask for upload a package for your version of Ubuntu. You can check which builds are available just checking the "Overview of published packages" section on the PPA main page.
E: Unable to locate package somepackage
If you didn't get the "Not Found" error when updating the package list, this means that the package maintainer has uploaded packages for your version of Ubuntu, but not that specific package. You can verify changing the "Published in: Any series" to your series name (ie. precise) and clicking the "Filter" button. If your package is not there but in other series, ask the package maintainer to upload a package to your specific version of Ubuntu.
Now remember, the PPA maintainers are humans, have a life and they are not getting paid to do this work (most of the time), if they haven't uploaded a package they may have their reasons, so keep this in mind.