Error "QIBASE driver not loaded" after 5.4.1 upgrade

[lqsa]

After upgrading from 5.4.0 to 5.4.1, my application gives an error when try to access to Firebird:

Warning: QSqlDatabase: QIBASE driver not loaded (kernel\qsqldatabase.cpp:781, void QSqlDatabasePrivate::init(const QString&))

But the driver is available:
Warning: QSqlDatabase: available drivers: QIBASE QSQLITE QMYSQL QMYSQL3 QODBC QODBC3 QPSQL QPSQL7 (kernel\qsqldatabase.cpp:782, void QSqlDatabasePrivate::init(const QString&))

[SGaist]

Hi,

What does QSqlDatabase::error() return ?