Update manager says it has been 14 days since last update, and I know that I have updated mor recently.

Ubuntu periodically runs update manager and I always install the updates. If memory serves, the last time this happened was around the 14th. An icon has appeared in the lower right corner of the screen which indicates that update information is outdated. I started the package manager and received the following error message:
W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ natty/partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_natty_partner_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ natty/partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_natty_partner_binary-i386_Packages)
W: Duplicate sources.list entry https://robin.powdarrmonkey.net/ubuntu/ maverick/ Packages (/var/lib/apt/lists/robin.powdarrmonkey.net_ubuntu_maverick_Packages)

Not sure how to proceed from here.