captcha in a belongs_to

Hi
    I am using simple_captcha. I have two models User and Staff.
Relation ship are

User has_one staff
staff belongs_to user

     Now in the staff edit I have to include a captcha. I did like

<% form_for @user, :url => staff_url(@staff), :html => {:method => :put
} do |f|%>
    <p>
      <%= f.text_field :first_name,:maxlength => 50 %>
    </p>
    <p>
      <%= show_simple_captcha :image_style => 'random',:distortion =>
'medium' %>
    </p>
<%end %>

   And in staff.rb
apply_simple_captcha :message => "Verification code does not match with
image."

  And in update action of of staff controller

  def update
    @staff = Staff.find(params[:id])
    @user = @staff.user
      if @staff.valid_with_captcha? and
@user.update_attributes(params[:user])
        flash[:notice] = "check your mail "
        redirect_to login_url
      else
        flash.now[:error] = @staff.errors.full_messages.join("<br />")
#This I wrote deliberately
        render :action => :edit
      end
  end

But even I put the correct captcha code and submit , it always shows
message
"Verification code does not match with image.". Dont know why please
help

Note:

       The params are like
{"user"=>{"first_name"=>"Tom", "last_name"=>""}, "action"=>"update",
"_method"=>"put",
"authenticity_token"=>"0OWRFPssTgTqCUESex7LrJ2QQ7HWSiAQxtiMhQm/N1s=",
"captcha"=>"PYESEZ", "id"=>"10", "controller"=>"staff"}

Thanks in advance
Tom

Hi
  Anybody please help. This still i can't solve

Tom