Just a heads up as to what I finally figured out what my problem was...(embaressed look time)...

In fact the very same thing happened again to me today and so I called somebody else in the house over to watch me to see what I might be doing wrong.

It turned out that I was accidently putting in my Render Rewards code into the COUPON CODE section in the cart instead of into the GIFT CERTIFICATE section.

I'm so used to using coupon codes whilst a gift cert is a bit of a rarity for me and so that I was in mental auto-mode filling in the cart fields which my observer picked up on pointing out what might be wrong. (after 3 attempts though)

So 'problem' (of my own making) solved! :-)

Thanks.