OK, for the benefit of all those reading here, this is my story
I called AMEX yesterday and advised the lass from Platinum Travel that the voucher was showing the expiry date had past. She had no idea what promo i was talking about, so I got her email address and send it to her. She then called Virgin whilst I was on hold - and they advised the voucher was working. She advised to call the Guest Centre and they would take care of it.
So I called the Guest Centre, and they advised that the voucher was valid - but it was only available for international flights! I told her to double check and she did, and said she could not help me at all.
At this point, I was furious and I called AMEX back - but Platinum travel had closed, and I was put through to Card Services. The guy I spoke to correctly identified the promo - but said he would have to escalate to AMEX Marketing. They could take 5 days to get back to me. I said fine.
However, as soon as I hung up I emailed the Platinum travel chick again and had a good whinge.
She called me the next morning and advised she had Virgin on the phone and they would book the flight for me. As we went through the booking with Virgin, the guy advised that as this was going to come through the contact centre, there would be an additional $15 booking fee. I almost lost it at him when I advised that I was more than happy to do it online, except the #$%&! voucher would not work!
He advised it should work online - and I kept him on the phone while I tried it - when i went to put in the expiry date as per my voucher email from AMEX, he advised that the expiry date was wrong! Instead of 22/11/2013 (which I believed most of us have), he advised it should be 31/10/2013.
So i tried it and hey presto! It worked! Anyway, I went back to the AMEX chick and advised her to cancel my escalation and to make a note as there are many others in the same boat as me! For what its worth - if you encounter this problem, try putting in an expiry date of 31/10/2012.
Good Luck