emacs25.1 + gnus, opening message gives: epg-error "no usable configuration" CM

[Gijs Hillenius <gijs@hillenius.net>]

Hi,

I just started using Debian Emacs 25.1 + Gnus to get to my email. There
is one message that gives an epg-error that I've not seen before, and
eh, it seems neither has Google (except for pointing me to the source
code)..

Following the error, the message is displayed as raw. The message is
displayed normally under Gnus in emacs24: there the message warns:
[[S/MIME Signed Part:Failed]]

The error suggests that I need to change/add settings to my Emacs init.el or
.gnus file? But what?

Here is the Backtrace. 

Debugger entered--Lisp error: (epg-error "no usable configuration" CMS)
  signal(epg-error ("no usable configuration" CMS))
  epg-context--make(CMS nil nil nil nil nil nil)
  epg-make-context(CMS)
  mml-smime-epg-verify(((#("multipart/alternative" 0 21 (boundary "Apple-Mail=athirdrandomnumber" buffer #<buffer  *mm*-284343> from "name@invalid" start nil)) (#<buffer  *mm*-592458> ("text/plain" (charset . "utf-8")) quoted-printable nil ("inline") nil nil nil) (#("multipart/mixed" 0 15 (boundary "Apple-Mail=_somerandomnumberB" buffer #<buffer  *mm*-435762> from "name@invalid" start nil)) (#<buffer  *mm*-694220> ("text/html" (charset . "utf-8")) quoted-printable nil nil nil nil nil) (#<buffer  *mm*-880244> ("application/vnd.oasis.opendocument.text" (name . "attachmentname") (x-unix-mode . "0644")) base64 nil ("attachment" (filename . "attachmentname")) nil nil nil) (#<buffer  *mm*-624164> ("text/html" (charset . "us-ascii")) 7bit nil nil nil nil nil))) (#<buffer  *mm*-696004> ("application/pkcs7-signature" (name . "smime.p7s")) base64 nil ("attachment" (filename . "smime.p7s")) nil nil nil)) (#("multipart/signed" 0 16 (micalg "sha1" protocol "application/pkcs7-signature" boundary "Apple-Mail=anotherrandomnumber" buffer #<buffer  *mm*-412231> from "name@invalid" start nil)) (micalg . "sha1") (protocol . "application/pkcs7-signature") (boundary . "Apple-Mail=anotherrandomnumber")))
  mml-smime-verify(((#("multipart/alternative" 0 21 (boundary "Apple-Mail=athirdrandomnumber" buffer #<buffer  *mm*-284343> from "name@invalid" start nil)) (#<buffer  *mm*-592458> ("text/plain" (charset . "utf-8")) quoted-printable nil ("inline") nil nil nil) (#("multipart/mixed" 0 15 (boundary "Apple-Mail=_somerandomnumberB" buffer #<buffer  *mm*-435762> from "name@invalid" start nil)) (#<buffer  *mm*-694220> ("text/html" (charset . "utf-8")) quoted-printable nil nil nil nil nil) (#<buffer  *mm*-880244> ("application/vnd.oasis.opendocument.text" (name . "attachmentname") (x-unix-mode . "0644")) base64 nil ("attachment" (filename . "attachmentname")) nil nil nil) (#<buffer  *mm*-624164> ("text/html" (charset . "us-ascii")) 7bit nil nil nil nil nil))) (#<buffer  *mm*-696004> ("application/pkcs7-signature" (name . "smime.p7s")) base64 nil ("attachment" (filename . "smime.p7s")) nil nil nil)) (#("multipart/signed" 0 16 (micalg "sha1" protocol "application/pkcs7-signature" boundary "Apple-Mail=anotherrandomnumber" buffer #<buffer  *mm*-412231> from "name@invalid" start nil)) (micalg . "sha1") (protocol . "application/pkcs7-signature") (boundary . "Apple-Mail=anotherrandomnumber")))
  mm-possibly-verify-or-decrypt(((#("multipart/alternative" 0 21 (boundary "Apple-Mail=athirdrandomnumber" buffer #<buffer  *mm*-284343> from "name@invalid" start nil)) (#<buffer  *mm*-592458> ("text/plain" (charset . "utf-8")) quoted-printable nil ("inline") nil nil nil) (#("multipart/mixed" 0 15 (boundary "Apple-Mail=_somerandomnumberB" buffer #<buffer  *mm*-435762> from "name@invalid" start nil)) (#<buffer  *mm*-694220> ("text/html" (charset . "utf-8")) quoted-printable nil nil nil nil nil) (#<buffer  *mm*-880244> ("application/vnd.oasis.opendocument.text" (name . "attachmentname") (x-unix-mode . "0644")) base64 nil ("attachment" (filename . "attachmentname")) nil nil nil) (#<buffer  *mm*-624164> ("text/html" (charset . "us-ascii")) 7bit nil nil nil nil nil))) (#<buffer  *mm*-696004> ("application/pkcs7-signature" (name . "smime.p7s")) base64 nil ("attachment" (filename . "smime.p7s")) nil nil nil)) (#("multipart/signed" 0 16 (micalg "sha1" protocol "application/pkcs7-signature" boundary "Apple-Mail=anotherrandomnumber" buffer #<buffer  *mm*-412231> from "name@invalid" start nil)) (micalg . "sha1") (protocol . "application/pkcs7-signature") (boundary . "Apple-Mail=anotherrandomnumber")) "name@invalid")
  mm-dissect-multipart((#("multipart/signed" 0 16 (micalg "sha1" protocol "application/pkcs7-signature" boundary "Apple-Mail=anotherrandomnumber" buffer #<buffer  *mm*-412231> from "name@invalid" start nil)) (micalg . "sha1") (protocol . "application/pkcs7-signature") (boundary . "Apple-Mail=anotherrandomnumber")) "name@invalid")
  mm-dissect-buffer(nil t)
  gnus-display-mime()
  gnus-article-prepare-display()
  gnus-article-prepare(1242 nil)
  gnus-summary-display-article(1242 nil)
  gnus-summary-select-article(nil nil pseudo)
  gnus-summary-scroll-up(1)
  funcall-interactively(gnus-summary-scroll-up 1)
  call-interactively(gnus-summary-scroll-up nil nil)
  command-execute(gnus-summary-scroll-up)