By Sylvia, did you mean you are using Linux Mint 18.3 with Ubuntu Xenial as the package base?
Although Linux Mint was derived from Ubuntu, we do not support distribution for such, So if you are using Sylvia via apt repository for the Ubuntu Xenial, I can advice you to please register again the apt repository by changing the part of $(lsb_release -cs) included in the following command to xenial.
sudo bash -c 'echo -e "deb http://archive.hark.jp/harkrepos $(lsb_release -cs) non-free\ndeb-src http://archive.hark.jp/harkrepos $(lsb_release -cs) non-free" > /etc/apt/sources.list.d/hark.list'
Previously registered URL (domain) of the apt repository will not be able to connect due to our server migration which may have been causing the error.
Installation Instruction for Linux
Best regards,
