debian Today, the installation error

[homodo]

# apt-get update
Get:1 http://security.debian.org lenny/updates Release.gpg [197B]
Hit http://security.debian.org lenny/updates Release
Get:2 http://ftp.de.debian.org lenny Release.gpg [386B]
Ign http://security.debian.org lenny/updates/main Packages/DiffIndex
Ign http://security.debian.org lenny/updates/contrib Packages/DiffIndex
Ign http://security.debian.org lenny/updates/non-free Packages/DiffIndex
Hit http://ftp.de.debian.org lenny Release
Hit http://security.debian.org lenny/updates/main Packages
Hit http://security.debian.org lenny/updates/contrib Packages
Ign http://ftp.de.debian.org lenny/main Packages/DiffIndex
Hit http://security.debian.org lenny/updates/non-free Packages
Ign http://ftp.de.debian.org lenny/contrib Packages/DiffIndex
Ign http://ftp.de.debian.org lenny/non-free Packages/DiffIndex
Hit http://ftp.de.debian.org lenny/main Packages
Hit http://ftp.de.debian.org lenny/contrib Packages
Hit http://ftp.de.debian.org lenny/non-free Packages
Fetched 2B in 2s (1B/s)
Reading package lists... Done
W: There is no public key available for the following key IDs:
4D270D06F42584E6
W: You may want to run apt-get update to correct these problems