How to troubleshoot errors after successful Drupal update?
According to this comment you should re-upload common.inc file in includes folder.


  I don't use Drupal Commons, but I got the same error when upgrading
  Drupal Crore from 7.20 to 7.34.
  
  This function was added in Drupal Core 7.33 so check your core version
  is later than that. https://www.drupal.org/node/2369141
  
  I then fixed it by reuploading common.inc in the includes folder. Must
  have not uploaded correctly the first time.