Anyone accepted travellers cheques?

hi all
I foolishly accepted an American Express travellers cheque in payment for a rental of our gite. The guests duly departed and I now find that neither my bank nor Banque de France will accept it. I have lost 500€.
Anyone any ideas please?

Speak to American Express directly.

I did that Mat. however they told me to post the cheque to their office in Salt Lake City and request payment from them by letter. I am reluctant to do this because once I send the cheque all I have as evidence is a photocopy of it.
I was rather hoping someone who has actually been through this process of accepting a travellers cheque would reply to my post.