If you add back your NNS-dapp principal as a controller, NNS-dapp will be able to fetch the details but as long as it isn’t a controller, it cannot.
You can find your principal in the “Settings” page (https://nns.ic0.app/settings/).
Yes I tried to do that:
dfx canister update-settings --add-controller <principal> <canister>
but got the error I posted above.
Also with --network ic as Severin pointed out?
(NNS Canister error when asking for details - #13 by Severin)
I actually asked but yes --network ic was put at the end after canister id.
I am using dfx -v 0.13.1 and I think I changed the principal with -v 0.12.1, not sure if that could be an issue.
I think I know what’s the problem, no controllers are attached to that particular canister.
If I open it in the dashboard, there are no controllers at all.
This could be because I tried to remove the project on the canister and this may have also removed the controller? Maybe this is expected behaviour. Again I am at the experimental stage so I could be doing something not right.
Is there anything I can do to rescue it or just rack it up to experience?
Thanks
Not sure what happened, not a dfx expert. Maybe @Severin will better guess.
At that stage my understanding is that nothing can be done as no one control the canister anymore, so no rescue possibility. That said, maybe Severin has some ideas.
He didn’t seem very confident but thanks for your help.
If it says 404 Canister not found then it is too late to do anything. If it said 403 Forbidden then the controllers would have been messed up, and then it could be possible to do something.
The replica returned an HTTP Error: Http Error: status 404 Not Found, content type “application/cbor”, content: Canister qrjtn-liaaa-aaaap-qa4pq-cai not found
Thanks for the confirmation. Weird that it still shows up in the nns-dapp. Maybe I should just un-link it and that will be that?
Yes, linking in the canister dapp just records the canister ID and then on page load will request its status. @peterparker, maybe you guys could make the error distinguish between a few common error cases? 404 for a deleted canister, and 403 for non-controller principals come to mind
I can see a long road of learning ahead. Thanks!
Why not adding it to the backlog. You know if these are documented somewhere or 404 and 403?
No, no real documentation exists for the codes. I’ve tried multiple times to get all these status codes and/or error codes (there can be different error codes under a HTTP 200 return code) documented somewhere and have gotten nowhere 
I’d really like to have a list somewhere for dfx and agent-rs…
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Gotcha. Added a task in the backlog.
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