Silly error... I don't (currently) use G+ on a daily basis, so this error message is a bit facile - I haven't even touched G+ today, so either the HN shared circle is too big, or it's reached it's own daily limit.

Edit: apparently the limit is 1000, so just add the shared circle from a posting that has < 1000 entries (like this one: https://plus.google.com/106419647632534512037/posts/DaWro5Hp... )