When adding a PPA in Ubuntu, the GPG key is imported using port 11371. If this port is blocked (by your ISP, Firewall) the GPG key import fails so you'll get lots of errors when running an update and also, the Update Manager doesn't install any available updates. But this will finally be fixed starting with Ubuntu 11.04 Natty Narwhal - an update to software-propreties notes that port 80 will be used by default instead of 11371 for getting the GPG keys.
Hopefully this "software-properties" feature will be backported to older Ubuntu versions; meanwhile you can use Launchpad Getkeys to fix the missing GPG keys.
Hopefully this "software-properties" feature will be backported to older Ubuntu versions; meanwhile you can use Launchpad Getkeys to fix the missing GPG keys.
