update manager crashes

[Gurudutt]

Distribution: Ubuntu 11.04 natty
Application: Ubuntu Tweak 0.5.12
Desktop: gnome

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/ubuntutweak/mainwindow.py", line 502, in setup_notebook
    page = module()
  File "/usr/lib/python2.7/dist-packages/ubuntutweak/modules/updatemanager.py", line 44, in __init__
    self.update_list()
  File "/usr/lib/python2.7/dist-packages/ubuntutweak/modules/updatemanager.py", line 59, in update_list
    PACKAGE_WORKER.update_apt_cache(init=True)
  File "/usr/lib/python2.7/dist-packages/ubuntutweak/common/package.py", line 226, in update_apt_cache
    self.cache = apt.Cache()
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 89, in __init__
    self.open(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 127, in open
    self._cache = apt_pkg.Cache(progress)
SystemError: E:Encountered a section with no Package: header, E:Problem with MergeList /var/lib/apt/lists/in.archive.ubuntu.com_ubuntu_dists_natty_main_binary-i386_Packages, E:The package lists or status file could not be parsed or opened.