Problem with Gnus moving mail

[ng0@n0.is]

Hi,

I seem to be unable to move messages with Gnus.

I made use of a config that used to work a while ago for myself,
and with 'enter group', 'mark message', B-m I get the following
error:

Debugger entered--Lisp error: (error "Trying to require a method that doesn’t exist")
  signal(error ("Trying to require a method that doesn’t exist"))
  error("Trying to require a method that doesn't exist")
  gnus-get-function((nil "") request-accept-article t)
  gnus-valid-move-group-p(nnml:torproject)
  #[(symbol) "\x7f	!\205	\nB\211\207" [predicate symbol out] 2](nnml:torproject)
  mapatoms(#[(symbol) "\x7f	!\205	\nB\211\207" [predicate symbol out] 2] [0 0 0 0 0 0 0 0 0 0 nnml:gnu\.emacs\.emacs-pretest-bug 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 nnml:gnu\.health\.dev 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ...])
  gnus-remove-if-not(gnus-valid-move-group-p [0 0 0 0 0 0 0 0 0 0 nnml:gnu\.emacs\.emacs-pretest-bug 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 nnml:gnu\.health\.dev 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ...] t)
  gnus-read-move-group-name("Move" nil (822011) "nnml:")
  gnus-summary-move-article(nil)
  funcall-interactively(gnus-summary-move-article nil)
  call-interactively(gnus-summary-move-article nil nil)
  command-execute(gnus-summary-move-article)

I've written more Guile than Elisp so far - how can I get started
debugging what's wrong here? For what it's worth, my version of
Emacs and Gnus is: GNU Emacs 25.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.21)
 of 2017-12-29
 running on Gnu GuixSD.

I can push my most recent Gnus config and include a link if that
helps.

Thanks
-- 
ng0 :: https://ea.n0.is
A88C8ADD129828D7EAC02E52E22F9BBFEE348588 :: https://ea.n0.is/keys/