[LAU] GPG error: debian-multimedia: The following signatures were invalid: NODATA 2

At 14:43 reloading data for the repositories was ok. I didn't changed anything, but at 14:51 I got an error, I reloaded the keyring, anyway, at 15:06 I still got this: W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://www.debian-multimedia.org squeeze Release: The following signatures were invalid: NODATA 2 W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://www.debian-multimedia.org wheezy Release: The following signatures were invalid: NODATA 2 W: Failed to fetch http://www.debian-multimedia.org/dists/squeeze/Release W: Failed to fetch http://www.debian-multimedia.org/dists/wheezy/Release W: Some index files failed to download. They have been ignored, or old ones used instead. Any ideas? Ralf