usrmerge on root NFS will not be run automatically

[Marco <lists@homerow.info>]

Hi,

I'm in the process of upgrading my Debian stable hosts and run into
a problem with usrmerge:

  Setting up usrmerge (35) ...

  Warning: NFS detected, /usr/lib/usrmerge/convert-usrmerge will not be run
  automatically. See #842145 for details.

  E: usrmerge failed.
  dpkg: error processing package usrmerge (--configure):
   installed usrmerge package post-installation script subprocess returned error exit status 1
  Errors were encountered while processing:
   usrmerge
  E: Sub-process /usr/bin/dpkg returned an error code (1)

True, root is mounted via NFS. So I ran usrmerge manually:

  root@foobar:~# /usr/lib/usrmerge/convert-usrmerge 

  FATAL ERROR:
  Both /lib/udev/rules.d/60-libsane1.rules and /usr/lib/udev/rules.d/60-libsane1.rules exist.

  You can try correcting the errors reported and running again
  /usr/lib/usrmerge/convert-usrmerge until it will complete without errors.
  Do not install or update other Debian packages until the program
  has been run successfully.

It instructs me to:

  You can try correcting the errors reported and running again

But it's not mentioned anywhere *how* to correct those errors. It's
true that both files exist. I've read

  https://wiki.debian.org/UsrMerge

But the page doesn't cover the error I face.

How to fix the error? Is there a command I can run (e.g. rsync?) to
fix whatever usrmerge complains about? Like keeping only the newest
file or deleting the old one? I feel there's very little info out
there how to recover from this situation. Any tips are much
appreciated.

Marco

Debian stable 6.1.0-11-amd64