Board Thread:Bug Reports/@comment-70.208.4.39-20160425212446/@comment-27516710-20160920065713

Still looks like a block ID conflict. Either the world is hosed or you have something conflicting with it. Even possible that the download is corrupted. I really wish the mod team would post ZIP files instead of JAR files because JAR files have bad tendency to download incomplete and then you get weird things happening when you try to execute them.

Also try creating a totally separate profile only with Forge (version 1.7.10) and only for the LOTR mod. Some people create a single Forge profile and then swap out mods and I've seen where this causes problems. For my LOTR profile I never use it for anything else. If I want to play a different mod pack I use another profile. This helps to ensure there's nothing from one mod leaving behind things that might conflict with another.