It looks like there may be an issue with the release-upgrader and how it checks mirrors to see if they are active / available and communicating via ftp. If you want to upgrade you might consider changing the communication method from ftp to http.
It looks like there may be an issue with the release-upgrader and how it checks mirrors to see if they are active / available and communicating via ftp. If you want to upgrade you might consider changing the communication method from ftp to http.