title: Amazon S3 CORS error
body: <p>I've been getting permission denied errors when my app requests files through Javascript on amazon S3. </p>
  
  <p>I have a CORS file set up and it seems to work most of the time, but fail intermittently. </p>
  
  <p>I can always solve this problem by clearing my browser cache. </p>
  
  <p>Any clues on what this could be? I'm not using cloudfront, which I know some people have found to cause a problem. </p>