nnir - Couldn't request group: Search produced empty results

[Sebastian Tennant]

Hi Gnus folk.

I've tried indexing my nnml folder with two different back ends;
swish-e and glimpse, and both result in the following message when I
type 'G-G' in the Group buffer, despite the fact that searches work
perfectly well on the command line:

 gnus-group-read-ephemeral-group: Couldn't request group: Search produced empty 
results.

In the case of swish-e I added the following to my ~/.gnus:

 (require 'nnir)
 (setq nnir-search-engine      'swish-e
       nnir-swish-e-index-file "/home/sebyte/.gnus.d/nnml-index.swish-e")

And for glimpse:

 (require 'nnir)
 (setq nnir-search-engine                'glimpse
       nnir-glimpse-home                 "/home/sebyte/.gnus.d/glimpse"
       nnir-glimpse-remove-prefix        "/home/sebyte/.gnus.d/nnml/"
       nnir-glimpse-additional-switches  '("-i" "-w"))

Am I simply missing something obvious? I hope not, because then I'm
going to feel very stupid indeed.  I fear that I am :-/

Sebastian

P.S. Apologies for posting this twice, but if I wanted any response I
     probably shouldn't have posted it in a barely related thread the
     first time.