1. emacs -Q
2. M-x ediff-regions-linewise, type RET twice to use *scratch* for both
   Ediff buffers (it doesn't matter which buffers are used).
3. Any attempt to mark a region, indeed it seems any further input at
   all, makes Emacs abort.  This is completely reproducible. Full
   backtrace attached. 

In GNU Emacs 24.0.50.7 (i686-pc-linux-gnu, GTK+ Version 2.18.6)
 of 2010-09-16 on escher
Windowing system distributor `The X.Org Foundation', version 11.0.10605000
configured using `configure  '--with-imagemagick' '--without-toolkit-scroll-bars''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t