Adding PPA's results in "Couldn't resolve host 'launchpad.net'"

Ah ... I've been caught out with this before! I've been trying to add the webupd8team PPA to my newly installed 12.04

I already had:

export http_proxy=

but webupd8team (and I think launchpad) need:

export https_proxy=

As others have said, you need to set HTTP_PROXY and HTTPS_PROXY but you also need to use the option '-E' to tell sudo to use the environment variables you've just set!

sudo -E add-apt-repository ppa:tualatrix/ppa

ref: How do I get add-apt-repository to work through a proxy?

It seems more like of the proxy problem. The server you are trying to connect to is not getting past through your connection because the proxy connection is refusing it. To get it right, Just close your proxy and they try re-running your program. Maybe that can help