Error message received after upgrading to WordPress 3.5 "Download Failed. Destination Directory For File Streaming Does Not Exist Or Is Not Writable" when trying to update plugins or install themes.
1. First you will want to FTP to your hosting.
2. Navigate to wwwrootwp-includes
3. Open the file CLASS-HTTP.PHP with notepad or an editor
4. Word wrap if necessary, search for the lines
if ( ! is_writable( dirname( $r['filename'] ) ) )
return new WP_Error( ‘http_request_failed’, __( ‘Destination directory for file streaming does not exist or is not writable.’ ) );
5. Once you find the lines, you may want to comment them out simply by adding // in front of the lines
6. Save the document. You should be able to install/update plugins.