Failure situation part-way through results in undefined result

If a batch fails, e.g. because of a missing folder, an error message is given about that folder, but the eventual result is not stated. The app should explicitly state what happened, so that people know what to re-upload or not.

We found that it looks like everything up to the failure point did get imported, plus (oddly) the one after it, but then subsequent ones didn't go in.