GPG error with new url

[Reto Kaiser <reto@retokaiser.com>]

Hi,

After I changed my backports entry in sources.list from "backports.org" to:
 deb http://backports.debian.org/debian-backports lenny-backports main

I get the following message when running "apt-get update":
 W: GPG error: http://backports.debian.org lenny-backports Release:
The following signatures were invalid: NODATA 2
 W: You may want to run apt-get update to correct these problems

Is this known? Am I doing something wrong?

Sincerely,
 Reto Kaiser


# apt-key list
/etc/apt/trusted.gpg
--------------------
pub   1024D/F42584E6 2008-04-06 [expires: 2012-05-15]
uid                  Lenny Stable Release Key <debian-release@lists.debian.org>

pub   4096R/55BE302B 2009-01-27 [expires: 2012-12-31]
uid                  Debian Archive Automatic Signing Key (5.0/lenny)
<ftpmaster@debian.org>

pub   2048R/6D849617 2009-01-24 [expires: 2013-01-23]
uid                  Debian-Volatile Archive Automatic Signing Key (5.0/lenny)

pub   1024D/16BA136C 2005-08-21
uid                  Backports.org Archive Key <ftp-master@backports.org>
sub   2048g/5B82CECE 2005-08-21

pub   4096R/B98321F9 2010-08-07 [expires: 2017-08-05]
uid                  Squeeze Stable Release Key
<debian-release@lists.debian.org>

pub   4096R/473041FA 2010-08-27 [expires: 2018-03-05]
uid                  Debian Archive Automatic Signing Key
(6.0/squeeze) <ftpmaster@debian.org>




# apt-cache showpkg debian-backports-keyring
Package: debian-backports-keyring
Versions:
2009.02.20 (/var/lib/apt/lists/backports.debian.org_debian-backports_dists_lenny-backports_main_binary-amd64_Packages)
(/var/lib/dpkg/status)
 Description Language:
                 File:
/var/lib/apt/lists/backports.debian.org_debian-backports_dists_lenny-backports_main_binary-amd64_Packages
                  MD5: 4ad7ba6540e2360e8780be59d371d2f9