I've been able to run org-edit-src-code just fine under NTEmacs
24.2.50.1 on Windows 7, but under GNU Emacs 23.2.1 on Debian, I got an
error:

    Wrong type argument: integer-or-marker-p, nil

With the attached patch, I've been able to run it on both systems. The
change passes (make-marker) to (copy-marker), instead of nil.

Kind Regards,
Mike Gauland