keep getting "GPG error" while doing update

["H.S." <hs.samix@gmail.com>]

Hi,

I have been getting this error since a week or two when I do apt-get update:
Fetched 3652kB in 20s (180kB/s)
Reading package lists... Done
W: GPG error: http://secure-testing.debian.net testing/security-updates
Release: The following signatures couldn't be verified because the
public key is not available: NO_PUBKEY 946AA6E18722E71E
W: GPG error: ftp://ftp.nerim.net etch Release: The following signatures
couldn't be verified because the public key is not available: NO_PUBKEY
07DC563D1F41B907
W: You may want to run apt-get update to correct these problems


I have tried:

 apt-key add /usr/share/apt/debian-archive.gpg
 apt-key add /usr/share/keyrings/debian-role-keys.gpg

but the warning doesn't go away. What other keys do I need to import?

thanks,
->HS
Debian Testing, kernel 2.6.12.