in your "reply" action, you defined @parent:
def reply @parent = Topic.find(params[:id]) end
but in your replyTopic action, you define "parent", which is a local variable, and not @parent: def replyTopic parent = Topic.find(params[:parentID]) @topic = Topic.new(params['topic']) .... .... end
therefore Rails has no @prent variable in the "reply.rhtml" view to fill the forms, and throws an error.
the problem should be simply fixed by changing "parent" into "@parent" in the replyTopic action