I received following error and then I tried apt-get update
to correct it but that didn't work.
W: Duplicate sources.list entry http://http.us.debian.org/debian/ wheezy/contrib i386 Packages (/var/lib/apt/lists/http.us.debian.org_debian_dists_wheezy_contrib_binary-i386_Packages) W: Duplicate sources.list entry http://http.us.debian.org/debian/ wheezy/non-free i386 Packages (/var/lib/apt/lists/http.us.debian.org_debian_dists_wheezy_non-free_binary-i386_Packages) W: You may want to run apt-get update to correct these problems