Apple has finally determined that some ATI x1900 XT cards (the big red ones) used in the original MacPro and the MacPro (8x) may have some issues. Cards with V6Z in the last 4 digits are subjected to a recall.
If you have an ATI card (check your system profiler), bring the card itself to an Apple Authorized Service Provider or an Apple Store for verification and exchange. If you have had the card replaced with another of like kind and paid for it, contact Apple for a refund.
More details are here.
Image courtesy of yourmacstore
