lilypond-book fails; python 2.3 used instead of 2.4

[Graham Percival]

lilypond-book produces pdfs with incorrect margins, and displays this  
error message:

---
Traceback (most recent call last):
  File  
"/Users/gperciva/Apps//LilyPond.app/Contents/Resources/bin/lilypond- 
book", line 1754, in ?
    main ()
  File  
"/Users/gperciva/Apps//LilyPond.app/Contents/Resources/bin/lilypond- 
book", line 1732, in main
    psfonts_file = os.path.join (global_options.output_name, basename +  
'.psfonts')
  File  
"/System/Library/Frameworks/Python.framework/Versions/2.3/lib/ 
python2.3/posixpath.py", line 62, in join
    elif path == '' or path.endswith('/'):
AttributeError: 'NoneType' object has no attribute 'endswith'
---
(although it keeps on processing the document)

I have python2.4 installed via fink, but it's still finding the system  
2.3 (at /usr/bin/python).  Any hints?

- Graham