Today, while updating my Debian Squeeze, after running

sudo aptitude update

I got this:

E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/ftp.debian.org_debian_dists_squeeze
_contrib_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.
E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/ftp.debian.org_debian_dists_squeeze
_contrib_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.

After googling a little, I found this solution.

sudo rm /var/lib/apt/lists/* -vf

This removed all the corrupted files, and the process could start again with no problems.

After that all was working again.