traceback for `make epub`

gistfile1.pytb

# Sphinx version: 1.1.2
# Python version: 2.6.6
# Docutils version: 0.8.1 release
# Jinja2 version: 2.5.5
Traceback (most recent call last):
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/cmdline.py", line 189, in main
    app.build(force_all, filenames)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/application.py", line 204, in build
    self.builder.build_update()
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/__init__.py", line 196, in build_update
    'out of date' % len(to_build))
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/__init__.py", line 252, in build
    self.write(docnames, list(updated_docnames), method)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/__init__.py", line 292, in write
    self.write_doc(docname, doctree)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/epub.py", line 284, in write_doc
    return StandaloneHTMLBuilder.write_doc(self, docname, doctree)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/html.py", line 416, in write_doc
    self.post_process_images(doctree)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/html.py", line 611, in post_process_images
    Builder.post_process_images(self, doctree)
  File "***/lib/python2.6/site-packages/Sphinx-1.1.2-py2.6.egg/sphinx/builders/__init__.py", line 134, in post_process_images
    if '?' in node['candidates']:
  File "***/lib/python2.6/site-packages/docutils-0.8.1-py2.6.egg/docutils/nodes.py", line 534, in __getitem__
    return self.attributes[key]
KeyError: 'candidates'