Atualizando para o Rails 2.3.2

app/controllers/attachments_controller.rb

@@ -89,7 +89,7 @@ class AttachmentsController < ApplicationController
 
 	def undelete
 		@attachment = Attachment.find_with_deleted(params[:id])
-		@attachment.update_attribute(:deleted_at, nil)
+		@attachment.recover!
 		flash[:notice] = 'Attachment restored'[]
 		AttachmentRestoreLogEntry.create!(:target_id => @attachment.id, :user => @current_user, :course => @attachment.course)
 		redirect_to course_attachment_url(@attachment.course, @attachment)