calibre doesn't start because of ImportError

Confirmed on one Intel based desktop i386.

Same error on Oneiric too...

$ calibre
Traceback (most recent call last):
  File "/usr/bin/calibre", line 18, in <module>
    from calibre.gui2.main import main
  File "/usr/lib/calibre/calibre/gui2/main.py", line 19, in <module>
    from calibre.library.database2 import LibraryDatabase2
  File "/usr/lib/calibre/calibre/library/database2.py", line 22, in <module>
    from calibre.library.caches import ResultCache
  File "/usr/lib/calibre/calibre/library/caches.py", line 16, in <module>
    from calibre.utils.search_query_parser import SearchQueryParser
  File "/usr/lib/calibre/calibre/utils/search_query_parser.py", line 21, in <module>
    from pyparsing import CaselessKeyword, Group, Forward, \
ImportError: Bad magic number in /usr/lib/calibre/calibre/utils/pyparsing.pyc

$ apt-cache policy calibre
calibre:
  Installed: 0.8.8+dfsg-1ubuntu1
  Candidate: 0.8.8+dfsg-1ubuntu1
  Version table:
 *** 0.8.8+dfsg-1ubuntu1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ oneiric/universe i386 Packages
        100 /var/lib/dpkg/status

$ file /usr/lib/calibre/calibre/utils/pyparsing.pyc
/usr/lib/calibre/calibre/utils/pyparsing.pyc: python 2.6 byte-compiled

$ md5sum /usr/lib/calibre/calibre/utils/pyparsing.pyc
0b25c93a2a40b14de8405b9c915cb888 /usr/lib/calibre/calibre/utils/pyparsing.pyc

$ lsb_release -rd
Description: Ubuntu 11.10
Release: 11.10

Found the solution here:

   http://osdir.com/ml/general/2011-08/msg19708.html

First you remove and purge calibre

sudo apt-get remove --purge calibre
sudo apt-get remove --purge calibre-bin

This fails to remove the lib folders so you have to do this manually as root

sudo rm -rvf /usr/lib/calibre

Then you re-install

sudo apt-get install calibre

This worked for me.