Comcast's CableCARD support gets a lot of (justifiable) flak. It's nice to see that, for once, they were on the ball and not at fault for the TiVo's interoperability issues. You could lay this one at TiVo tech support's doorstep; but it's also possible that your problem was an outlier since we still don't know exactly what the cause was. At any rate, congratulations on your persistence; hope you will find it was worth the effort in the end. And thanks for posting the details here for posterity's sake.