Why has the download from audible stopped working?

Why has the download from audible stopped working?
I have been an Audible subscriber for a couple of years and my books automatically downloaded to iTunes Library from where I could copy them to my ipod. I stopped my subscription for a few months as I had got behind. When I rejoined this month, I've bought an audio book and can download it but it's not appearing iTunes Library. What has gone wrong and how can I sort this?

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