Many times it's showing "update info is outdated" and when I'm trying to update this is the details of error message (which is the heading of this thread) I'm getting:-
W:GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A9A06AEF9CB8DB0, W:Failed to fetch http://ppa.launchpad.net/deluge-team/ppa/ubuntu/dists/trusty/main/binary-amd64/Packages 404 Not Found, W:Failed to fetch http://ppa.launchpad.net/deluge-team/ppa/ubuntu/dists/trusty/main/binary-i386/Packages 404 Not Found, E:Some index files failed to download. They have been ignored, or old ones used instead.
Any doughnut Ubuntu mates? [grin]