Apabila saat update di ubuntu muncul error

Contoh error :
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com maverick Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster>

W: GPG error: http://deb.opera.com stable Release: The following signatures were invalid: BADSIG F9A2F76A9D1A0061 Opera Software Archive Automatic Signing Key 2010 <packager>
W: GPG error: http://download.virtualbox.org maverick Release: The following signatures were invalid: BADSIG 54422A4B98AB5139 Oracle Corporation (VirtualBox archive signing key) <info>
W: GPG error: http://archive.ubuntu.com maverick Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster>
W: GPG error: http://archive.getdeb.net maverick-getdeb Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A8A515F046D7E7CF
W: GPG error: http://packages.medibuntu.org maverick Release: The following signatures were invalid: BADSIG 2EBC26B60C5A2783 Medibuntu Packaging Team <admin>
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/maverick/Release

W: Failed to fetch http://ppa.launchpad.net/techm3/outr...86/Packages.gz 404 Not Found

W: Some index files failed to download, they have been ignored, or old ones used instead.

> Kemudian masukan kode key 

$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 16126D3A3E5C1192 54422A4B98AB5139 F9A2F76A9D1A0061 40976EAF437D05B5 2EBC26B60C5A2783 A8A515F046D7E7CF

> kemudian:
$ sudo -i
# apt-get clean
# cd /var/lib/apt
# mv lists lists.old
# mkdir -p lists/partial
# apt-get clean
# apt-get update