Since installing drop-box (whether this had any bearing I don't know) I have this error with any installation or update using the software centre or command-line using apt-get.
E: GPG error: http://ppa.launchpad.net wily InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
Prior to this event I have been installing/updating without problems, and I have checked many, many posts in various forums (ubuntuforums.org, answers.launchpad.net, bugs.launchpad.net, askubuntu.com) and while those errors look similar all of the answers posted have failed to resolve the problem. While their problems were dealt with they don't seem to apply in this case. I am using a wired ethernet connection and there is no problem with this in any other respect.
Not sure if it is a network proxy problem, but my system worked earlier anyhow. The drop-box download added some repositories but I have tried removing them, manually deleting the /var/lib/apt/lists/* files, the drop-box files from /etc/apt/sources.list.d/, changing the download repositories and so on but without any success.
Thanks, Nick
