Summary: My X1 system suddenly developed the XRE-00021 and 3059 errors. The problem was caused by the local Xfinity store, and a subsequent visit to the store got the problem fixed. The call center couldn't help, and it was not a wiring or signal problem. It was an "activation" problem.
I am writing this detailed post because error XRE-00021 seems to have a split personality in the forums. "ComcastAndrew" usually says it is a signal problem, ie the lowest possible layer, pure hardware, maybe a wiring or splitter problem, and "RickGr4" tends to point people towards some kind of activation or provisioning problem, ie the highest layer. I would be the last one to doubt "ComcastAndrew" who has helped so many, but in my case it was an activation problem.
"Digital Adapter $0.50
This Equipment Is Inactive. to Avoid Future
Charges, Please Return The Equipment to Your
Nearest Service Center."
The words above on our bill led to a problematic Saturday. About 5 years ago we stopped using the std def TV that was serviced by a small DTA adapter. Then we lost the DTA. Recently I found it, and called the call center to see if they really wanted it back or would they just tell me to forget it. After 15 minutes on the phone they still weren't really convinced that I was authorized to talk to them. It was also taking me 3 minutes to fight through the "Do you want to return your unused equipment" script when I called the call center. So I decided to return the little box to the local store.
The guy at the store gave me a receipt for the box and I went home. When I got home, my 2 year old X1 master box and 2 satellites would not tune to any station, and were giving the XRE-00021 error.
Called the call center and got a guy in Minnesota. We went through the usual resets and remove-the-plug reboots with no effect. He then sent me to "Level 2", which was a nice lady in India. She looked up the error and found that it was a signal or wiring problem and would I please check all my wires. I told her my wiring was fine before I went to the store, and can't you figure out what happened to my "activation"? She seemed pretty immune to this argument, and continued to focus on the box and wiring. She then said she would perform a procedure that would take an hour, and she would call me back. And by the way you still have an unused DTA on your account.
I've always had good luck at the stores, and so drove back. The rep told me he saw two problems: My device heirarchy or "stacking" wasn't right, and the DTA was still on the account. He addressed both. He looked at the call center notes on my ticket, and said what they were doing was unlikely to help.
When I got home the problem was fixed.
So this XRE-00021 error can have wildly different root causes. My account was "activated" just fine until it wasn't. Call center people only have access to the wiring or signal explanation, while my rep at the store said lots of little things on the account can cause problems. Thanks to RickGr4 for persistently pointing people towards the "activation" role. Recommend that the internal database of errors be updated so that call center people can be more helpful with this error.