svn copy results in "Couldn't determine absolute path"

[Wim Coenen <wc...@gmail.com>]

I have a subversion server up and running as an apache module.
All client operations work fine, EXCEPT any commits after I have done
a "svn copy" or "svn mv". For those commits I get this error:

Couldn't determine absolute path of '\\\\foo\\bar\\baz\\svn'

(where '\\\\foo\\bar\\baz\\svn' matches the path to my
repository, as configured in httpd.conf)

The apache server is running as the windows user "svnadmin"
which has full access to the repository data. If I configure the
server to run as administrator, or give "svnadmin" full
"domain administrator" rights, then the problem completely
disappears. Of course this is not a desirable solution: I would like
to give minimal rights to "svnadmin" to do its job.

So what am I missing here? What is it that the server account needs
so that is can also handle "svn copy" commits?

This seems to be exactly the same problem as described by
http://svn.haxx.se/users/archive-2005-10/0654.shtml
But that question went unanswered.

Thanks in advance,
Wim.

More details:

====================================
Versions
====================================
Subversion 1.4.0
Apache 2.0.59
mod_auth_sspi 1.0.4
Hosted on Windows 2000

=====================================
The apache log contains the following errors:
=====================================
[Mon Sep 25 11:40:29 2006] [error] [client 172.16.1.51] Could not
MOVE/COPY /repository/!svn/bc/38/branches/WIC/file-in-WIC-branch.txt.
[500, #0]
[Mon Sep 25 11:40:29 2006] [error] [client 172.16.1.51] Unable to make
a filesystem copy.  [500, #125001]
[Mon Sep 25 11:40:29 2006] [error] [client 172.16.1.51] Couldn't
determine absolute path of '\\\\foo\\bar\\baz\\svn'  [500, #125001]
[Mon Sep 25 11:40:29 2006] [error] [client 172.16.1.51] (OS 87)The
parameter is incorrect.  : authentication failure for
"/repository/!svn/act/fc6a2674-766e-8a4b-aac5-dc042b2f94ed": user
unknown, reason: cannot generate context

(note that the last authentication failure may be unrelated: I have
read that it is the
SSPI module trying to use the "guest" account, which is normal and automatically
retried with the server account)

=============================
relevant section from apache httpd.conf
=============================
<Location /repository >
  DAV svn
  SVNPath //foo/bar/baz/svn

  # always require logon, even for readonly access
  Require valid-user

  AuthName "R&D Subversion repository"
  # Authentication with the windows domain controller
  AuthType SSPI
	SSPIAuth On
  	SSPIAuthoritative On
  	SSPIDomain mydomainname
	SSPIOfferBasic On
	# simplify username as passed to svn for fine grained access control
	SSPIOmitDomain On
	SSPIUsernameCase lower

  # For any operations other than these, require the user to be in the
  # "Baz Developers" group.
  <LimitExcept GET PROPFIND OPTIONS REPORT>
     Require group "Baz Developers"
  </LimitExcept>

</Location>

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