Problem with sudo apt get update: The repository cdrom... does not have a Release file

apt updates

To resolve this problem from terminal you must remove/comment this CD-ROM repository source directly from /etc/apt/sources.list

 sudo nano /etc/apt/sources.list

and comment or remove lines that include cdrom. eg:

deb cdrom:[Ubuntu-Server 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.3)]/ xenial main restricted

Try this:
Open Software & Updates and in the Ubuntu Software tab uncheck Cdrom with Ubuntu 16.04 LTS 'Xenial Xerus' under the section Installable from CD-ROM/DVD.

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