Gift Audiobook Media Files Missing after iPhone sync

Hi All

I recently received an Audiobook as a gift, I happily redeemed this into my iTunes 11 and synced it onto my iPhone. So far so good.

However when I returned to iTunes, the audiobook appears to exist but if I try to play it, iTunes it says it cannot find the media files and invites me to locate them myself. I cannot find them either. However the book is still there on my iPhone. The purchase shows as a gift in my account but being an Audiobook I can't re-download. All this took place before the next TimeMachine cycle so there is no backup except on the phone.

Any ideas how I recover from this error condition?

Many thanks