How to remove edit lock on a node in Drupal

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Sometimes you receive an error "The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved." .

The above error means

1) Either the problem is related to two users editing the same node
2) Or it can be related to max_input_vars in your php.ini

Solutions:

1) Clear cache of your browser
2) Edit php.ini file. Usually its located on /etc/php5/apache5/apache2/php.ini. Then find max_input_vars and increase it. Dont forget to restart the Apache server. If you are using suhosin then you also needs to change its values.

You can also change it with .htaccess file so that you dont need to restart the server:

php_value max_input_vars 2000 

If you are using suhosin you also need to add few more lines:

php_value suhosin.get.max_vars 2000
php_value suhosin.post.max_vars 2000
php_value suhosin.request.max_vars 2000