SB6121 D3 modem no longer supported?

I upgraded to a D3.1 modem a few months ago and stashed my old SB6121 in the closet. Hating to

sit on otherwise useful equipment, I put the modem on craigslist, and mentioned that it would be

good for the bottom tiers on Cox. Buyer tried to provision it and was told it couldn't be used, so I

had to refund the buyer. So, Is the SB6121 garbage now? or at LEAST on Cox? Should I throw it away,

despite the fact it works FINE (at least it did when I took it out of service...)