GPG Key error upon aptitude update

The error message looks like :

W: GPG error: http://security.debian.org etch/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9AA38DCD55BE402B

Solution:-

as root

#gpg --keyserver subkeys.pgp.net --recv-keys 9AA38DCD55BE402B

we will get this message

gpg: directory `/root/.gnupg' created
gpg: can't open `/gnupg/options.skel': No such file or directory
gpg: keyring `/root/.gnupg/secring.gpg' created
gpg: keyring `/root/.gnupg/pubring.gpg' created
gpg: requesting key 55BE402B from hkp server subkeys.pgp.net

gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key 55BE402B: public key "Debian Archive Automatic Signing Key (5.0/lenny) " imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)

next do:-

#gpg --armor --export 55BE302B | apt-key add -

then try aptitude update again