When update crashes I got this message:
W:Failed to fetch http://cran.at.r-project.org/dists/precise-backports/main/source/Sources 404 Not Found
E:Some index files failed to download. They have been ignored, or old ones used instead.
When update crashes I got this message:
W:Failed to fetch http://cran.at.r-project.org/dists/precise-backports/main/source/Sources 404 Not Found
E:Some index files failed to download. They have been ignored, or old ones used instead.
I think your link is wrong, try this one
deb http://cran.at.r-project.org/bin/linux/ubuntu precise/