My first work day meet this problem. Invalid Username/Password in my DBDesigner 4 connection. Then I found this page, let me quote it.
Bug or What?
Well, for the first time using the DBDesigner you may encounter the “dbExpress: Invalid Username/password” message. We don’t know what the ‘bug’ is.
Searching the Internet, the solution is to reset the MySQL password using the following command. You can use similar or current MySQL password for user root in this case. The following example shows the MySQL root user. Change accordingly to other user and the host (here we use localhost). It is done through MySQL Command Line Client console.
SET PASSWORD FOR ‘root’@’localhost’ = OLD_PASSWORD(‘your_old_root_password_or_same_password’);
If the previous step successful, all MySQL databases in the localhost will be listed