Cannnot authenticate debian archive packages

[Enrique Perez-Terron <enrio@online.no>]

Today I installed some 30 packages, but got an error message from two of
them: samba and swat. They could not be authenticated. I tried to look
around for a problem, but I could only find that if I downloaded the
files manually, the md5sum was as detailed in /var/lib/apt/lists/
security.debian.org_dists_etch_updates_main_binary-amd64_Packages.

Then I tried to install gui-apt-key, but I got the same message.
Downloading the deb manually and checking the md5sum against the
Packages file, the match was perfect.

Any ideas?

My sources.list:
deb  http://ftp.uk.debian.org/debian/ etch         main contrib non-free

deb     http://ftp.debian.org/debian/ etch         main contrib non-free
deb-src http://ftp.debian.org/debian/ etch         main contrib non-free
deb     http://security.debian.org/   etch/updates main contrib non-free