Can you post your entire Forge log file in a pastebin, so that we may see what all mods are being loaded?
Mod edit: Attachments are disabled on this forum.
I've written up a tutorial on setting up ForgeGradle with IntelliJ IDEA and Scala on my blog at http://minalien.com/tutorial-setting-up-forgegradle-for-intellij-idea-scala/