Problem solved.

My original code was:

m_Db.addDatabase("QMYSQL");

It have to be:

m_Db = QSqlDatabase::addDatabase("QMYSQL");

In the first case

bool ok = m_Db.open();

even if driver il correctly loaded.

Now I have a different proble, if I run directly the program, it is able to connect to the remote database. If I run it inside debugger, I receive this error:

"Open database failed: Can't create TCP/IP socket (10106) QMYSQL: Unable to connect"

Someone know how to configure debugger so to avoid this error?

Thank you.