Roundcube enable password change , but not working

Hi ,
I have installed ispconfig and using roundcube, i have tried to enable password change on round cube
Step by step that i have done :
1. vi /etc/roundcube/config.inc.php
$config['plugins'] = array('password');
2. vi /etc/roundcube/plugins/password/config.inc.php
$config['password_db_dsn'] = 'mysql://ispconfigassword@localhost/dbispconfig';
$config['password_query'] = 'UPDATE mail_user SET password=%c WHERE email=%u LIMIT 1';

Then i am tried to change password on rouncube and i got "Cannot save new password" on bottom right .

Please help me

 

Have you installed Roundcube plugin for ISPConfig?
Or are you using ISPConfig at all?