Replacing all occurrences of archive.ubuntu.com and security.ubuntu.com with old-releases.ubuntu.com in the etc/apt/sources.list file was the missing piece of the puzzle to get the pesky warning triangle to disappear from the upper panel in my no-longer-supported Ubuntu 10.04 Lucid Lynx installation. Thank you!
Replacing all occurrences of archive.ubuntu.com and security.ubuntu.com with old-releases.ubuntu.com in the etc/apt/sources.list file was the missing piece of the puzzle to get the pesky warning triangle to disappear from the upper panel in my no-longer-supported Ubuntu 10.04 Lucid Lynx installation. Thank you!