[Bada Bing]

I have Debian 6.0 64 bit. I installed the calibre package. I'd like to use ebook-convert with recipes, but I get the following error:

Traceback (most recent call last):
  File "/usr/bin/ebook-convert", line 18, in <module>
    from calibre.ebooks.conversion.cli import main
  File "/usr/lib/calibre/calibre/__init__.py", line 16, in <module>
    from calibre.startup import plugins, winutil, winutilerror
  File "/usr/lib/calibre/calibre/startup.py", line 52, in <module>
    set_translators()
  File "/usr/lib/calibre/calibre/utils/localization.py", line 66, in set_translators
    lang = get_lang()
  File "/usr/lib/calibre/calibre/utils/localization.py", line 27, in get_lang
    from calibre.utils.config import prefs
  File "/usr/lib/calibre/calibre/utils/config.py", line 710, in <module>
    prefs['installation_uuid'] = str(uuid.uuid4())
  File "/usr/lib/calibre/calibre/utils/config.py", line 490, in __setitem__
    return self.set(key, val)
  File "/usr/lib/calibre/calibre/utils/config.py", line 501, in set
    return self.__config.set(key, val)
  File "/usr/lib/calibre/calibre/utils/config.py", line 445, in set
    src = self.option_set.serialize(opts)+ '\n\n' + footer + '\n'
  File "/usr/lib/calibre/calibre/utils/config.py", line 376, in serialize
    for name in [None] + self.group_list]
  File "/usr/lib/calibre/calibre/utils/config.py", line 359, in render_group
    self.serialize_opt(getattr(opts, pref.name, pref.default))))
  File "/usr/lib/calibre/calibre/utils/config.py", line 367, in serialize_opt
    from PyQt4.QtCore import QString
ImportError: No module named PyQt4.QtCore

When I ask, aptitude says:

python-qt4 is already the newest version.
libqt4-core is already the newest version.

Can you help me what might be the problem?