It's likely that the specific PPA you are trying to reach there is outdated, or discontinued based on the error message you are receiving.
Pop open a terminal and navigate to
Find the offending PPA and delete the file.
If your apt list is stopping at a certain object, it will then fail to reach the end of the list, meaning you may be missing out on some upgrades for packages that are further along in the sources.list
EDIT: This page, https://launchpad.net/~chicharreros/+archive/ppa seems to suggest support only goes as high as Ubuntu 11.04 which may be why you're having issues