Hello v3xx, Thank you for trying to help. I tried the command line code you had given me then I restarted my computer. But again, the same error message appeared when I tried to check on system updates as stated below:
W:The repository 'cdrom://Ubuntu-MATE 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215) xenial 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 configuration details., W:http://www.openprinting.org/download/printdriver/debian/dists/lsb3.2/Release.gpg: Signature by key F8897B6F00075648E248B7EC24CBF5474CFD1E2F uses weak digest algorithm (SHA1), E:Failed to fetch cdrom://Ubuntu-MATE 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215)/dists/xenial/main/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs, E:Some index files failed to download. They have been ignored, or old ones used instead.
This message has appeared everytime I have tried for updates since I first installed Ubuntu Mate 16.04.2 64-bit.