It looks like the first one is an intermittent error that can occur due to an intermittent error from an upstream service. That shouldn't break saving on ZoteroBib (since the actual data, when it works, comes from somewhere else), and we'll fix that. But just retrying a few times should work.
The second ISBN isn't registered in any mainstream ISBN database (and the only Google result is this forum thread).
The second ISBN isn't registered in any mainstream ISBN database (and the only Google result is this forum thread).