I recently upgraded my System76 Gazelle Pro to Ubuntu 16.04. (More accurately, I completely wiped the SSD and performed a complete fresh install).
Every time the software updater runs, it tells me that I am not connected to the internet, even though a few updates will complete.
Delving further, I discovered this error message:
W:The repository 'cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1) trusty Release' does not have a Release file.,
W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use.,
W:See apt-secure(8) manpage for repository creation and user**
Any suggestions?