If you get a black screen after Forge modloader loads, your libarys could have corropted. There are links to those files in the log, you can paste them into your broser and your browser should download it.
There would be a list of mods approved and if the mod is not on the list it would warn the user that the mod doesn't valiated. And an option to turn off.
THIS
[sEVERE] [ForgeModLoader] The mod Railcraft (Railcraft) requires mod versions [Forge@[4.1.4.287,)] to be available
2012-10-01 15:42:16
And also you need to download newwest version of forage from jenkins.
You probily get cookie jars mixed up.