It first happend about a week ago that I received this error message the first time. It shows up daily.
W:Failed to fetch http://de.archive.ubuntu.com/ubuntu/dists/natty/multiverse/source/Sources 404 Not Found [IP: 141.30.13.30 80] , E:Some index files failed to download. They have been ignored, or old ones used instead.
I can do updates from other ppa as usual. I noticed that problem in relation to special ppa defined by the user, but I can't imagine that natty's multiverse could be down for days.
Is there something I can check on my system to solve this?
You could try changing the server that you attempt to connect to for Multiverse (and other) updates.
Open Synaptic Package Manager and click on Settings > Repositories, then in the dropdown selection that is labeled "Download From:" choose Other. Click the "Select Best Server" button, and after it has run some speed tests and chosen one for you, click "OK" or "Choose Server."
Update your package lists -- either click Reload in Synaptic, or in terminal type
Hopefully this will allow you to grab new Multiverse updates!