Comment 2 for bug 533549

This interrupted the upgrade from karmic to lucid (I'm sorry, I don't have exactly how logged). A manual reinstall attempt at the commandline gave me:

Setting up yaml-mode (0.0.4-2) ...
emacsen-common: Handling install of emacsen flavor emacs
emacsen-common: Handling install of emacsen flavor emacs23
emacsen-common: byte-compiling for emacs23
Wrote /etc/emacs23/site-start.d/00debian-vars.elc

In debian-run-directories:
debian-startup.el:131:25:Warning: `mapcar' called for effect; use `mapc' or
    `dolist' instead
Wrote /usr/share/emacs23/site-lisp/debian-startup.elc
install/yaml-mode: Handling install for emacsen flavor emacs23
ln: creating symbolic link `./yaml-mode.el': File exists
emacs-package-install: /usr/lib/emacsen-common/packages/install/yaml-mode emacs23 emacs23 failed at /usr/lib/emacsen-common/emacs-package-install line 30, <TSORT> line 2.
dpkg: error processing yaml-mode (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 yaml-mode
E: Sub-process /usr/bin/dpkg returned an error code (1)

which I'm assuming is the same failure the upgrader hit. Purging and then reinstalling got past this.