QimageReader Unknown Error

HI Friends,
I have problem with QImageReader,
QImageReader reader("/disk/system.jpg");
qDebug()<<"Error Message: "<<reader.errorString();
Its displaying "Unknown error "
As i am using Qt 4.3 embedded version.
QImageReader::UnknownError 0 An unknown error occurred. If you get this value after calling read(), it is most likely caused by a bug in QImageReader.

Please any one Help me to resolve this issue.

Thanks for replay,

I am calling image = reader.read();
qDebug()<< "Error Msg:"<<reader.errorString();
Here its displaying unknownSupported format message for JPEG images other images its working fine.
Can u tell me what might be the problem.

My requirement is i want to save any kind of image(and any resolution ) from one format to other format with scalling of 512x192 .