I get the same problem on first install since today. Download seems to be broken. I managed to install the plugin getting the tar.gz from macromedia and using "sudo dpkg-reconfigure flashplugin-nonfree" pointing to local directory contening flash compressed file.
-- flashplugin-nonfree does not install https://launchpad.net/bugs/50284 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
