Unable to use `package-refresh-contents`: Bad signature from GNU ELPA Signing Agent

[Nicky Chorley]

Hi all,

I'm running Emacs 25.3.1 on Slackware Linux 14.2 and `M-x
package-refresh-contents` is giving the following error:

Failed to verify signature archive-contents.sig:
Bad signature from 474F05837FBDEF9B GNU ELPA Signing Agent
<elpasign@elpa.gnu.org>
Command output:
gpg: Signature made Fri 08 Feb 2019 10:15:04 PM GMT using DSA key ID 7FBDEF9B
gpg: BAD signature from "GNU ELPA Signing Agent <elpasign@elpa.gnu.org>"

I don't recall changing anything in my config recently. Just to see if
that was causing a problem, I did remove my config (.emacs and
.emacs.d), but the problem persisted.

Any ideas about what's causing this?

Thanks,

Nicky Chorley