[Koha] Getting error-site library does not exist

During installation of koha on Ubuntu 12.04 LTS, I have found 1 error message.... when I have given command.... "sudo a2ensite library" I got a error "ERROR: Site library does not exist! Now problem is that I am able to run both Koha staff client and OPAC from the host computer i.e from my computer but i can't access my koha staff client from any other computer on my LAN network although I am able to access my koha OPAC using the ip address of my LAN network. Please help and solve the issue.