E: Failed to fetch cdrom://Ubuntu 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)/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.
Errors were encountered while processing:
libsimgearcore2017.3.1:amd64
E: Sub-process /usr/bin/dpkg returned an error code (1)