I have a single user that, trying to access Roundcube, get following error:
DATABASE ERROR: CONNECTION FAILED!
Unable to connect to the database!
Please contact your server-administrator.
It's a single user to get it:

DATABASE ERROR: CONNECTION FAILED!
Unable to connect to the database!
Please contact your server-administrator.
It's a single user to get it:
- for any other user on the server (on different domains,or even of the same domain) Roundcube works fine
- the user who get this error on Roundcube can work without issues on Horde or Squirrelmail