I had a problem connecting mysql from DBDesigner4. Error occurs :

Connection to database failed.

dbExpress Error: Invalid
Username/Password

Username/Password spelled correctly. The problem is because DBDesigner4 was designed for MySQL 3.x.x. For MySQL 4 and higher we have to do the old password trick. This is the solution which is works fine for me. In your terminal, connect to your database:

mysql -u root -p
SET PASSWORD FOR 'root'@'localhost' = OLD_PASSWORD('r00tp45sw0rd');
UPDATE mysql.user SET Password = OLD_PASSWORD('r00tp45sw0rd') WHERE Host = 'localhost' AND User = 'root';
FLUSH PRIVILEGES;

Then you should have no problem connecting to your MySQL servers. You may change the username (root), password (r00tp45sw0rd) & host (localhost) with your own.

* Updated [13/07/2007] – Thanks Raphael.