Problem with Installer

I downloaded The Long Road mod through its UK mirror, clicked on the setup, but the following message came up:

"NSIS Error: The installer you are trying to use is corrupted or incomplete. This could be the result of a damaged disk, a failed download or a virus. You may want to contact the author of this installer to obtain a new copy. It may be possible to skip this check using the /NCRC command line switch (NOT RECOMMENDED)."


And I have absolutely no idea what to do. I don't know what installer it is so I can't contact the author, and knowing nothing of computers I have no idea what they're talking about with the /NCRC command line switch. Help! :help: