diff --git a/app/controllers/attachments_controller.rb b/app/controllers/attachments_controller.rb
index 182a37453..026a12e9a 100644
--- a/app/controllers/attachments_controller.rb
+++ b/app/controllers/attachments_controller.rb
@@ -173,7 +173,7 @@ class AttachmentsController < ApplicationController
 
     respond_to do |format|
       # modify by nwb
-      if @attachment.container.is_a?(Course) || @attachment.container.course
+      if !@attachment.container.nil? && (@attachment.container.is_a?(Course) || @attachment.container.course)
         if @course.nil?
           format.html { redirect_to_referer_or forum_memo_path(@attachment.container.forum, @attachment.container) }
         else
@@ -286,7 +286,7 @@ private
     raise ActiveRecord::RecordNotFound if params[:filename] && params[:filename] != @attachment.filename
     if @attachment.container_type == 'Course'
       @course = @attachment.course
-    elsif @attachment.container.has_attribute?(:course) && @attachment.container.course
+    elsif  !@attachment.container.nil? && (@attachment.container.has_attribute?(:course) || @attachment.container.has_attribute?(:course)) && @attachment.container.course
       @course = @attachment.container.course
     else
       unless @attachment.container_type == 'Bid' || @attachment.container_type == 'HomeworkAttach' || @attachment.container_type == 'Memo' || @attachment.container_type == 'Softapplication'