An error occurred! Could not save new password.

[rcuser1]

What i did?
http://roundcubeskins.net/helpdesk/knowledgebase.php?article=16&rated=1

How do I enable password changing in Roundcube?
The password changing functionality in Roundcube is provided by the "password" plugin. You can enable the plugin by adding it to the "plugins" array of your config/config.inc.php, like this:

$config['plugins'] = array('xskin', 'password');

When the plugin is enabled, the users can change their email password by logging in to Roundcube and going to Settings / Password.

After this error message come out:
An error occurred! Could not save new password.

Why i Came here? Because of this:

[SKaero]

The document you followed lacks all the necessary information to actually setup the password plugin. Try reading the README file in the password plugin folder.