Weired render action question! help!

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