Run this command and see if it clears up the problem:
sudo rm /var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_natty_main_binary-i386_Packages
Run this command and see if it clears up the problem:
sudo rm /var/lib/ apt/lists/ us.archive. ubuntu. com_ubuntu_ dists_natty_ main_binary- i386_Packages