/usr/lib/mono/4.5/System.Runtime.Remoting.dll is in libmono-system-runtime4.0-cil 4.6.2.7+dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/4.5/../gac/System.Runtime.Remoting/4.0.0.0__b77a5c561934e089/System.Runtime.Remoting.dll