Board Thread:LotR Mod Technical Support/@comment-217.80.163.26-20191213144108/@comment-106.201.50.65-20191217155348

Is it the jopt-simple-4.5.jarfile? I had that problem too. Its a Mac related issue. The link's top answer will fix that hopefully.

https://www.reddit.com/r/MinecraftForge/comments/dg5q53/failed_to_download_file_the_file_contents_differ/