Comcast TBSHD channel not authorized. Pairing issue.
I just had this problem appear suddenly. TBSHD had been working fine on my Roamio Plus for a year, then suddenly (right before a NCAA basketball game no less), I got the not authorized error.
Comcast tech came out and replaced the cablecard, re-paired numerous times, etc still getting the same error. Called TiVo who had us go through a number of things regarding cablecard pairing, status, signal strength, SNR levels, etc. Still no TBSHD, all other channels fine. Comcast tech went through and measured all signals, etc and all was good.
After about 3 hours of debugging, the Comcast Tech got a call from his supervisor stating that just a few days earlier (about the same time I lost TBSHD), the Comcast engineers had made a "tweak" to TBSHD on the Comcast head end. They pushed updates to all of their Comcast set top boxes, so things were fine there, but they now realize there is an incompatibility with TiVos. Tech said that the supervisor would be working with TiVo to resolve the issue. We'll see, but at least we know what the problem is/was.
Update today 3/25/2015: TBSHD is now working again, so Comcast made some update on their head end I would guess.
BTW, it was extremely frustrating to hear the Comcast tech constantly berate TiVo...haven't seen anyone use a TiVo in years....blah blah blah. So glad the problem ended up being on Comcast's side of things after hours of hearing that it had to be TiVo since Comcast was fine.