[racket] using scribble --pdf on Windows

On Windows 7, I have had no trouble using scribble --html.  For the
first time in 5.1.3 I tried using scribble --pdf, and it does not
work.  Does anyone recognize whether I'm doing something wrong?

ventoux ~/Desktop/r/sk/tycs> scribble --pdf doc.scrbl
run-pdflatex: did not generate a log file at doc.log

 === context ===
C:\Program Files
(x86)\Racket\5.1.3\collects\scribble\private\run-pdflatex.rkt:25:2:
loop
C:\Program Files
(x86)\Racket\5.1.3\collects\scribble\private\run-pdflatex.rkt:7:0:
core
C:\Program Files
(x86)\Racket\5.1.3\collects\scribble\private\indirect-renderer.rkt:38:8:
for-loop
C:\Program Files (x86)\Racket\5.1.3\collects\scribble\run.rkt:105:0: build-docs
C:\Program Files (x86)\Racket\5.1.3\collects\scribble\run.rkt: [running body]

The problem can't be with finding the pdflatex executable, because the
expression used in scribble/private/run-pdflatex.rkt finds it fine:

> (or (find-executable-path "pdflatex")
              (and (eq? 'windows (system-type))
                   (find-executable-path "pdflatex.exe")))
#<path:C:\Program Files (x86)\MiKTeX 2.9\miktex\bin\pdflatex.exe>

Anyone else seeing this problem?

Shriram