Yep...been having the same problem for about a week now. E-mailed AltaVista a number of times about it and kept getting very unhelpful responses. Finally got a useful response tonight! --

Quoted from AV e-mail:
"When you are attempting to redeem for an item and experience difficulty, please attempt the redemption again.

If you continue to experience difficulties, we can process a manual redemption for you. We would need to know your full name, shipping address, e-mail used on your Rewards account, the item description and
the quantity of each item you would like to redeem for.

We can manually process your redemption and you will receive an email confirmation once the redemption has been processed. If you have any further questions, please feel free to contact us again.

Regards,

AltaVista Support Team"

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Then went back to the AltaVista site and attempted the redemption again... and "BEHOLD" --- it actually worked this time! :-Q