rcsdiff fails on Windows accessing Unix RCS files

I've got prebuilt executables for RCS 5.7 on a Windows machine and am
trying to work with files that are on an NFS server and accessed via a
Windows network drive.  I set RCSINIT to ",v/" so that the RCS files are
found from the working file names and I set RCS_LF_ONLY to handle the
Unix line endings.

rlog works fine, but rcsdiff fails right after printing the header:

c:\Documents and Settings\onc04664>"c:/Program Files/RCS 
5.7/bin/win32/rcsdiff.exe" -r1.22 h:/emacs/minibuffer-complete-cycle.el
"c:/Program Files/RCS 5.7/bin/win32/rcsdiff.exe" -r1.22 
h:/emacs/minibuffer-complete-cycle.el
===================================================================
RCS file: h:/emacs/RCS/minibuffer-complete-cycle.el,v

c:\Documents and Settings\onc04664>echo %ERRORLEVEL%
echo %ERRORLEVEL%
2

c:\Documents and Settings\onc04664>

There is a diff.exe program (version 2.7.1) in the same directory as the
RCS executables, but the GnuWin32 directory with diff.exe version 2.8.7
is before that in my PATH.

Is this a known problem?  Is there a workaround?

-- 
Kevin Rodgers
Sr. Software Engineer, IHS