Because you have thrown the error into the forum without any formatting. It is very difficult to read the error. Please use a pastebin url (saves on space on the forum and makes it easy to read the error).
From what I can tell. It seems like SpongeForge is conflicting with another mod. What that other mod is I dont know.
Some people have fixed this by using SpongeBootstrap ( SpongeBootstrap - Fixes ordering issue with other coremods ) but it is best to find the mod that is being the issue and remove it.