Did you check the comments section to see if anyone else had the same issue? Maybe the author took it down to do some work on it.
With that said, there's a little bug with Fallout where you try and download a mod from the in game mod menu but it won't let you. What you need to do is go to Bethesda.net, find the mod and add and remove it from your library a bunch of times from the website. Make sure to end that process with it being added to your library.
Then load up the game, go to the mods section, find the mod and try downloading it again. If it still doesn't work you could try repeating the process I just outlined again. If it still doesn't work for ya, than I'm stumped, might be that the mod is being worked on by the author.