Splitting this off issue829.  Thanks for the report, Simon!  

Echoing Jason's query: were these repositories converted separately?

Also, in the future, please open a new bug rather than reanimate somebody else's
dead one. I've been flip-flopping on what the right thing to do here is, and I
think generally speaking new bug is the way to go because it's less confusing. 
Watch a future me retract this :-)

msg6440 repeated below
----------------------
Reopening this bug, as I have one that looks a bit similar. The 
http://zwiki.org/ZWiki and http://zwiki.org/ZWiki-unstable repos have just been 
converted to darcs-2 format, from darcs-1 and hashed formats respectively. 
Pulling between them now gives the error. This is using darcs 2.1.0pre2 (+ 14 
patches) on ubuntu.

$ darcs pull
Pulling from "/repos/ZWiki"...
darcs: bug in get_extra commuting patches:
First patch is:
Sat May 17 10:14:34 PDT 2008  Simon Michael <simon@joyful.com>
  * clean up test rules
Second patch is:
Fri Oct 24 22:22:46 PDT 2008  Simon Michael <simon@joyful.com>
  * update makefile checklists, note new CHANGES.txt suffix

Hi Simon, I realise it's been since August that we last talked about
this, but I can I ping you on this?

Do you remember if the repositories were converted separately, or did
you merge, convert and unmerge?

Is there anything useful for you in
http://wiki.darcs.net/Troubleshooting#bug%20in%20get_extra%20commuting%20patch

Hi Eric.. sorry, I've tried and can't reconstruct what I did. Let's assume 
I converted separately, and refocus this issue on "pulling between 
independently-converted copies of a repo gives an uninformative error 
message".

On Wed, Apr 07, 2010 at 22:20:57 +0000, Simon Michael wrote:
> Hi Eric.. sorry, I've tried and can't reconstruct what I did. Let's assume 
> I converted separately, and refocus this issue on "pulling between 
> independently-converted copies of a repo gives an uninformative error 
> message".

Thanks. Sorry for the mess.

Unfortunately, I don't think there really is meaningful way to check to
see if repositories were independently converted.  If you think I'm
missing something (which I well may be), please check with the others
on IRC and open a new ticket.

Meanwhile, I'm marking this presumed-dead as we just don't have the
information we need to get a grasp of the problem.

-- 
Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow>
PGP Key ID: 08AC04F9