Have you tryed remove the /var/cache/apt/pkgcache.bin and runned
apt-get update?
Possible you have a bad file... caused by some energy fail or some
like.
[]s
--
O T A V I O S A L V A D O R
---------------------------------------------
E-mail: otavio@debian.org UIN: 5906116
GNU/Linux User: 239058 GPG ID: 49A5F855
Home Page: http://www.freedom.ind.br/otavio
---------------------------------------------