bug#38017: 26.1; Tramp: File not found and directory write-protected

[Markus Triska]

I am using Tramp to access remote files, and it works.

Specifically, I can access a remote server s with

    C-x C-f /ssh:s: RET

However, I am now in a situation where, when I do this, Tramp emits:

    File not found and directory write-protected

even though it worked perfectly just a moment ago in the same Emacs
instance.

When I start a new Emacs process, it works as expected in that instance.
Therefore, I think everything is correctly configured, but there is
something wrong in the existing instance that I would like to find and
correct so that I can continue using Tramp in the existing Emacs
instance.

Seeing that everything works when Tramp is freshly loaded, I did:

    M-x tramp-cleanup-all-connections RET

and then I unloaded Tramp with:

    M-x tramp-unload-tramp

>From this state, is there anything I can do to re-enable Tramp in this
existing Emacs? I will then try it with increased logging verbosity.

Thank you and all the best,
Markus

In GNU Emacs 26.1 (build 1, x86_64-apple-darwin15.3.0, X toolkit, Xaw scroll 
bars)
 of 2018-09-22 built on mt-mbpro
Windowing system distributor 'The X.Org Foundation', version 11.0.11502000