The recipe for Forbidden & Arcanus Iron Chain is the same as the recipe for vanilla chains, making it impossible to craft vanilla chains through a crafting table. However, vanilla chains can be created through the Mechanical Crafter, but not the Forbidden & Arcanus Iron Chains

Fixed on 1.2:
Fixed a recipe conflict between forbidden arcanus and ..vanilla minecraft
Now, the recipe will craft a vanilla chain, and you can put the vanilla chain alone in the crafting grid to get 3 F&A chains