Problem:

When I check for updates, I get a “Failed To Download Repository Information” error.

This is what comes up under details:

W: Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_natty_main_source_Sources Hash Sum mismatch,
E: Some index files failed to download. They have been ignored, or old ones used instead.

Solution:

Just remove the content of /var/lib/apt/lists directory:

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

then run:

sudo apt-get update