odd svn diff behavior

Preparing to do a merge, I wanted to check diffs, and ran into trouble.
Here are some examples; I apologize for the long lines and word
wrapping.
In brief, I'm getting "Delta source ended unexpectedly" or "A path under
version control is needed for this operation" for things that I think
should work.

Can anyone tell me what I'm missing? (subversion 1.06)

ross@iron:/usr/local/src/boost/boost/boost/smart_container$ svn diff
--new http://localhost/svn/mspath/trunk/src/boost/smart_container/
ptr_set_adapter.hpp
svn: Delta source ended unexpectedly
ross@iron:/usr/local/src/boost/boost/boost/smart_container$ svn diff
--old . --new
http://localhost/svn/mspath/trunk/src/boost/smart_container/
ptr_set_adapter.hpp
svn: Delta source ended unexpectedly
ross@iron:/usr/local/src/boost/boost/boost/smart_container$ svn diff
--old . --new
http://localhost/svn/mspath/trunk/src/boost/smart_container/
svn: Delta source ended unexpectedly
ross@iron:/usr/local/src/boost/boost/boost/smart_container$ svn diff
-rPREV:HEAD http://localhost/svn/mspath/trunk/src/boost/smart_container/
svn: A path under version control is needed for this operation
ross@iron:/usr/local/src/boost/boost/boost/smart_container$ svn diff
-rPREV:HEAD
http://localhost/svn/mspath/trunk/src/boost/smart_container/ptr_set_adapter.hpp
svn: A path under version control is needed for this operation

I have some vendor code in my current directory, and used part of it in
the directory in the URL. The URL was pasted directly from my browser
viewing the repository.

Note that the earlier exercises are attempting to compare a file
obtained from one part of the subversion tree with a version of the file
in a different part of the hierarchy.

I tried other variations not show here, including a space after the -r.

-- 
Ross Boylan                                      wk:  (415) 502-4031
530 Parnassus Avenue (Library) rm 115-4          ross@biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 476-9856
University of California, San Francisco
San Francisco, CA 94143-0840                     hm:  (415) 550-1062
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