error during sudo apt-get upadate
 

I got this error.
during sudo apt-get update
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GPG error: http://download.virtualbox.org lucid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 54422A4B98AB5139Failed to fetch cdrom://Ubuntu 10.04 LTS _Lucid Lynx_ - Release i386 (20100429)/dists/lucid/main/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Failed to fetch cdrom://Ubuntu 10.04 LTS _Lucid Lynx_ - Release i386 (20100429)/dists/lucid/restricted/binary-i386/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Failed to fetch http://ftp.debian.org/dists/sarge/ma...-i386/Packages 404 Not Found
Some index files failed to download. They have been ignored, or old ones used instead.
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some GPG error is coming. I think i need to fetch GPG public key but i don't know how to do this...

See here: Importing Authentication Keys