GPG cannot import public key

[helices]

GPG version trying to import: gpg (GnuPG) 2.0.14

Header from shared armored public key: Version: Encryption Desktop 10.3.0
(Build 8741)

GPG error on import:

# gpg --import /tmp/imps.asc

gpg: key 845F5188: no valid user IDs

gpg: this may be caused by a missing self-signature

gpg: Total number processed: 1

gpg:           w/o user IDs: 1

Other GPG import:

# gpg --allow-non-selfsigned-uid --import /tmp/imps.asc

gpg: key 845F5188: accepted non self-signed user ID "Concerto Support Key <
concerto.support at impact-ps.com>"

gpg: key 845F5188: public key "Concerto Support Key <
concerto.support at impact-ps.com>" imported

gpg: Total number processed: 1

gpg:               imported: 1  (RSA: 1)

Then:

# gpg --list-keys 845F5188

pub      0s/845F5188 2013-03-05

uid                  Concerto Support Key <concerto.support at impact-ps.com>

# gpg --edit-key 845F5188

gpg (GnuPG) 2.0.14; Copyright (C) 2009 Free Software Foundation, Inc.

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

pub     0s/845F5188  created: 2013-03-05  expires: never       usage: SC

                     trust: unknown       validity: unknown

[ unknown] (1). Concerto Support Key <concerto.support at impact-ps.com>

Command> sign

User ID "Concerto Support Key <concerto.support at impact-ps.com>" is not
self-signed.  Unable to sign.

Nothing to sign with key 31A070A8

No matter how I try, I cannot encrypt a file using that public key, even
using --edit-key to assign trust:

gpg: 845F5188: skipped: Unusable public key

gpg: /tmp/test.txt: encryption failed: Unusable public key



The owner of the public key insists that it is self-signed; but, our GPG
cannot find the self-signature

What am I missing?

Please, advise. Thank you
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