The unofficial third party repository Debian Multimedia stopped using the domain debian-multimedia.org some months ago. The domain expired and it is now registered again by someone unknown to Debian. (If we're wrong on this point, please sent us an email so we can take over the domain! ;) )

This means that the repository is no longer safe to use, and you should remove the related entries from your sources.list file.

After all, the need of an external repository for multimedia related packages has been greatly reduced with the release of Wheezy, which features many new and updated codecs and multimedia players.

Not sure if you're using the debian-multimedia repository? You can easily check it by running:

grep -i debian-multimedia.org /etc/apt/sources.list /etc/apt/sources.list.d/*

If you can see debian-multimedia.org line in output, you should remove all the lines including it.