title: WordPress 3.9 upgrade fails
body: <p>When I try to upgrade a WordPress 3.8.1 site to 3.9, I get the following error:</p>
  
  <p>The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.: wp-admin/includes/update-core.php</p>
  
  <p>Installation Failed</p>
  
  <p>I've checked all the folders and files in the site, and they all the same permissions.</p>
  
  <p>WordPress is running on Windows Server 2008 R2.</p>
  
  <p>Must I go through the manual upgrade process, or is they a way to tell why I'm getting this error message?</p>