I did try the first sudo command in terminal. The updates were found, but not installed, producing the same error in the earlier attached image. I did, however, find a fix in a different thread (https://bugs.launchpad.net/ubuntu/+bug/209093). I ran both at the same time, unfortunately, so I'm not sure which command fixed the problem, but my system can now update itself.
** Changed in: ubuntu Status: Incomplete => Invalid -- cannot update anything https://bugs.launchpad.net/bugs/209034 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs