Cannot redeclare drupal_get_hash_salt() I had a site and it was running fine on the live server but when I moved it to my local server it gave me this error. 

Fatal error: Cannot redeclare drupal_get_hash_salt() (previously declared in 
D:\wamp\www\htdocs\projects\mysite\includes\bootstrap.inc:2248) in 
D:\wamp\www\htdocs\projects\mysite\includes\common.inc on line 5045


I guess the problem occurred because of editing the variable

$drupal_hash_salt = 'zU4q79TqFe0thQO-xGQbfbrFfKloUk9OYXfQ70J1nw0';


manually in setting.php file.

Does anybody have any idea how can I solve this problem?
You've got definitely a Drupal upgrade problem, drupal_get_hash_salt used to be in common.inc and was moved to bootstrap.inc in Drupal 7.23 version as you can see in https://www.drupal.org/node/1739986.

Something went wrong with your core update, I'd suggest you to backup your data and upgrade your files to the latest version, then run update.php and check everything is OK.