ediff-buffers on Win7

Windows 7 GNU Emacs 24.2.1:

When I run ediff-files, it works.

When I try ediff-buffers to compare two files I'm already editing, I get 
this in a ediff-errors buffer:

Files c:\Users\IBM_AD~1\AppData\Local\Temp\file2.txt and 
c:\Users\IBM_AD~1\AppData\Local\Temp\file2.txt differ

It doesn't open the ediff buffer or display differences.

~~

The messages file says:

Computing differences between file1.txt and file2.txt ...
ediff-prepare-error-list: Errors in diff output.  Diff output is in 
#<buffer *ediff-diff*>

~~

I can view the temp directory in a command windows, using the IBM_AD~1 
path name.