Notice: Constant DATE_RFC7231 already defined in includes/bootstrap.inc on line 258

Notice: Constant DATE_RFC7231 already defined in includes/bootstrap.inc on line 258

Drupal 7:

• Open /includes/bootstrap.inc
• Go to line number 258
• Comment out the following line
  //define('DATE_RFC7231', 'D, d M Y H:i:s \G\M\T');
• Then add following line
  if (!defined('DATE_RFC7231')) {
  define('DATE_RFC7231', 'D, d M Y H:i:s \G\M\T');
  }
• Save and you are good to go 🙂