plugin qjpegd4.dll is loaded successfully but I fail to display a .jpg in a widget

QT 4.5.2
WINDOW 7
VS2005
add in 1.1.4

I use QPluginLoader to load the qjpegd4.dll
QPluginLoader::isLoaded() return ture
but I can not display a .jpg in a widget (other imageformats such as bmp and png work well)
QImage image("pic.jpg");
ui.widget->setImage(&image);

in show output from debug it says
qjpegd4.dll No symbols loaded.

what did I miss?

Regards,

Please show us your real code, because a widget does not have a setImage function. Also Qt will load the plugin, if it is in the right path, by itself. Maybe the problem is that you load the plugin.

I delete the code for loading the plugin.
And I put the imageformats fold into my project's debug fold.
Then it works well.

Maybe I should set the QTDIR environment while I am using the QT add-in.