MySQL access problem

[Paco Ros]

Hi all! :-)

I've got all mysql 5 related packages installed in a up to date dapper:
paco at blackbox:~$ dpkg -l "*mysql*" | grep ^ii | awk '{print $2}'
libdbd-mysql-perl
libmysqlclient12
libmysqlclient14
libmysqlclient15
mysql-admin
mysql-admin-common
mysql-client
mysql-client-5.0
mysql-common
mysql-query-browser
mysql-query-browser-common
mysql-server
mysql-server-5.0
php5-mysql
python-mysqldb
python2.4-mysqldb

I can create a user to access roundcubemail database (I've already created it) 
as usually:
paco at blackbox:~$ sudo mysql
Password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 6 to server version: 5.0.18-Debian_6-log

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> GRANT ALL PRIVILEGES ON roundcubemail.* TO rcm@'localhost' IDENTIFIED 
BY 'password' WITH GRANT OPTION;
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye

But I can't access to database:
paco at blackbox:~$ mysql -u rcm -p roundcubemail
Enter password:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket 
'/var/run/mysqld/mysqld.sock' (13)

I've not found any log errors (neither syslog nor mysql.* logs).
I've also tried it by using "blackbox" (my hostname) and "%" (all hosts) 
unsuccesfully.

Please, could anybody tell me what I am doing badly?

Thanks in advance for your help.
Kind regards.
-- 
Paco Ros.