Problem loading plugins throught generated bundle

Hi everybody, I've gereted my application bundle with the deployqt tool. When I'm on my mini Mac OS X 10.4.6 Tiger PowerPC G4) it work fine but when I test it on an onther mini Mac OS X 10.4.10 Tiger PowerPC G4, I always have the following error:
QSqlDatabase: QIBASE driver not loaded

Note that I'm using Qt plugins for firebird and they are located on Application.app/Contents/Plugins.

Does anyone have an idea about this problem and give the solution.
Best Reguards, Mourad