Any error similar like
“W: GPG error: http://my.archive.ubuntu.com feisty-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key
“
Try to edit /etc/apt/sources.list
Change all
http://my.archive.ubuntu.com
to
http://archive.ubuntu.com
http://my.archive.ubuntu.com is the repositories server for Malaysia.