error during apt-get update

["SENTHIL KUMAR" <nucleic81@gmail.com>]

I get this error wen i do a apt-get update.... ???
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Reading package lists... Done
W: GPG error: http://www.debian-multimedia.org etch Release: The
following signatures couldn't be verified because the public key is
not available: NO_PUBKEY 07DC563D1F41B907
W: Duplicate sources.list entry http://ftp.iitm.ac.in etch/main
Packages (/var/lib/apt/lists/ftp.iitm.ac.in_debian_dists_etch_main_binary-i386_Packages)
W: You may want to run apt-get update to correct these problems
root@saisha:/auto/home2/sen#
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