When I try to install/update any plugin from Help -> Install New Software I receive error messages like this:
No repository found at http://download.eclipse.org/releases/galileo.
or
Unable to connect to repository http://pydev.org/updates/site.xml
Invalid argument
This happens with all Eclipse versions.
I use Eclipse on Debian Sid.
Try disabling proxies inside Eclipse. This helped me once.
Here are some generic eclipse error resolution steps I use:
1) Try run eclipse with the -clean option. This should cleanup some stuff. No clue if it helps with your problem, but maybe worth a try?
2) Delete .metadata directory (or move it temporarily away) from your workspace and run eclipse with the -clean option again.
3) (Skip if you have tried this) Try download another eclipse installation into another local directory and try to see if that works out of the box. If it works, your former eclipse installation was bugged. If it does not work, I suggest checking your general network access to the specific urls you mention.
I had the same problem, try running eclipse with these options: -vmargs -Djava.net.preferIPv4Stack=true
It worked for me