"Invalid editor anchoring" error during diff

I'm getting an error message that I don't understand from subversion
1.0.4. The error message is:

        svn: Invalid editor anchoring; at least one of
        the input paths is not a directory and there was
        no source entry

I'm confused because the repository URL I'm specifying _is_ for a
directory, and the URL works with the "log" and "list" commands.

Here's a command line transcript, with the error at the bottom:

[Zephyr:~] samalone% svn --version
svn, version 1.0.4 (r9844)
    compiled May 22 2004, 06:40:24

Copyright (C) 2000-2004 CollabNet.
Subversion is open source software, see http://subversion.tigris.org/
This product includes software developed by CollabNet
(http://www.Collab.Net/).

The following repository access (RA) modules are available:

* ra_dav : Module for accessing a repository via WebDAV (DeltaV)
protocol.
   - handles 'http' schema
* ra_local : Module for accessing a repository on local disk.
   - handles 'file' schema
* ra_svn : Module for accessing a repository using the svn network
protocol.
   - handles 'svn' schema

[Zephyr:~] samalone% svn log --verbose -r1206:1247
svn://whirlwind/trunk/Projects/Life%20Balance/Conduit
------------------------------------------------------------------------
r1209 | samalone | 2004-05-22 22:35:16 -0400 (Sat, 22 May 2004) | 2
lines
Changed paths:
    A /trunk/Projects/Life Balance/Conduit/Mac/HotSyncIcons.r

HotSync icons missing from CVS, converted to text format.

------------------------------------------------------------------------
r1230 | samalone | 2004-05-25 14:02:14 -0400 (Tue, 25 May 2004) | 1 line
Changed paths:
    M /trunk/Projects/Life Balance/Conduit/Mac
    M /trunk/Projects/Life Balance/Conduit/Mac/Source
    M /trunk/Projects/Life Balance/Mac
    M /trunk/Projects/Life Balance/Mac/Prefix
    M /trunk/Projects/Life Balance/Mac/Sources
    M /trunk/Projects/Mac/Interface
    M /trunk/Projects/Mac/Interface/(prefix)
    M /trunk/Projects/Mac/Platform
    M /trunk/Projects/Mac/Platform/(prefix)

Added svn:ignore properties for generated files
------------------------------------------------------------------------
[Zephyr:~] samalone% svn diff -r1206:1247
svn://whirlwind/trunk/Projects/Life%20Balance/Conduit
svn: Invalid editor anchoring; at least one of the input paths is not a
directory and there was no source entry

Any ideas on why this is happening? My real goal is to merge these
changes into another branch, but I get the same error when I attempt
the merge. I assume that if I can resolve the diff error then I will
resolve the merge error as well.

--Stuart A. Malone
   Llamagraphics, Inc.