workbench cannot connect to DB server (but phpMyAdmin can)

[Silvano Fumagalli]

I have mysql insatlled un a lubuntu machine sice a few weeks and it was working correctly.
Yesterday I insatlled a new version of a demo PHP applciation and today I found that workbench cannot connect to the database.
On the contrary the server is working, I can use normally the php demo application anc I can use phpMyAdim to access to the various tables.

Only workbencj is not working. It has a strange startup behaviour. Instad of waiting in the first "welcome" dialog, it goes directly to the "Workbench central"
The connection test fails with the message "Can't connect to MySQL server on '120.0.0.1' (111)

I did not change anything in the configuration files after the upload of the new application and I wonder if the application itself could have changed something.

Here is a copy of the log file:
--------
[Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
[Note] - '0.0.0.0' resolves to '0.0.0.0';
[Note] Server socket created on IP: '0.0.0.0'.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
[Note] Event Scheduler: Loaded 0 events
[Note] /usr/sbin/mysqld: ready for connections.
Version: '5.5.34-0ubuntu0.13.10.1' socket: '/var/run/mysqld/mysqld.sock' port: 3306 (Ubuntu)
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
------------------

Could you advice nme howto solve this issue?
Thanks, Silvano