Inline file upload error: undefined method `size='

Hello,

I followed the tutorial at: http://khamsouk.souvanlasy.com/2007/5/1/ajax-file-uploads-in-rails-using-attachment_fu-and-responds_to_parent

However, in my controller I am getting the error:

NoMethodError (undefined method `size=' for #<SwfImage:0x5705b48>)

Other references to this error indicate that the render method is trying to render a string (which does have a size method) but it's attempting to render the SwfImage object instead. So how would I get around this? Any help would be appreciated.

#### VIEW CODE ####

<% form_for(:swf_image, :url => formatted_swf_images_path(:format => 'js'), :html => { :multipart => true, :target => 'upload_frame' }) do | f> %>   <p>     <b>Filename</b><br />     <%= f.file_field :uploaded_data %>   </p>

  <p>     <%= f.submit "Create" %>   </p> <% end %> <iframe id="upload_frame" name="upload_frame" style="width:1px; height: 1px; border:0px;" src="about:blank"></iframe>

#### CONTROLLER CODE ####

  def create     @swf_image = SwfImage.new(params[:swf_image])

    respond_to do |format|       if @swf_image.save         flash[:notice] = 'Image was successfully saved.'         format.html { redirect_to(@swf_image) }         format.js do           responds_to_parent do             render :update do |page|               page.insert_html :bottom, "swf_images", :partial => 'swf_images/image', :object => @swf_image               page.visual_effect :highlight, "image_#{@swf_image.id}"             end           end         end       else         format.html { render :action => "new" }         format.js do           responds_to_parent do             render :update do |page|               # do nothing             end           end         end       end     end   end