Duplicate sources.list entry

When I run "apt-get update" I am getting the following error:

W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ lucid/partner Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_lucid_partner_binary-i386_Packages)
W: You may want to run apt-get update to correct these problems

I have checked the /etc/apt/sources.list file and there aren't any duplicates it in. However, in the file /etc/apt/sources.list.d/lucid-partner.list, I found the line:

deb http://archive.canonical.com/ubuntu lucid partner

Which is a match to a line in the /etc/apt/sources.list file. I commented out the line in the lucid-partners.list file and now the "apt-get update" command completes without and error.

My question is simple: did I do the right thing, or is this a symptom of something else?