The error message contains:
Failed to fetch updates
This may have been caused by external, manually added software repositories or a corrupted sources file.
W: The repository 'http://ppa.launchpad.net/mpstark/elementary-tweaks-daily/ubuntu 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