Ubuntu 11.10 Upgrade to 12.04 - Release Upgrade Tool fails to complete download
I am new to ubuntu and unix systems and am trying to install ubuntu 12.04 on my system via the update-manager. My 11.10 version is current and checks have been made prior to clicking the update button for 12.04. However when the Release Update Tool is downloading it appears to fail to complete and get to the next stage of the process.
I have tried doing the install from the command line and it appears to be going well following entry of do-release-upgrade (Release Update Tool completes download) but fails with the following messages: -
>>> /etc/sudoers.d/sew_sudoers: too many levels of includes near line 25 <<<
sudo: parse error in /etc/sudoers.d/sew_sudoers near line 25
sudo: no valid sudoers sources found, quitting
Any help anyone can offer would be appreciated.