QFile not readable

[seux]

Hello out there,
i am trying to read from a file that the user chooses via a QFileDialog, but after that the file is not readyble...

file = new QFile(QFileDialog::getOpenFileName(....));
if(file.isReadable() != true)
{
     //This gets executed
     QMessageBox msg(QMessageBox::Information, "DEBUG", "File not readable", QMessageBox::Ok);
     msg.show();
     return;
}

file = new QFile(QFileDialog::getOpenFileName(....));
if(file.isReadable() != true)
{
     //This gets executed
     QMessageBox msg(QMessageBox::Information, "DEBUG", "File not readable", QMessageBox::Ok);
     msg.show();
     return;
}

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The interesting thing is, that the messagebox never really appears. But when I start the programm in the debugger i can see step by step that the code in the if condition gets executed and that the messgebox is not complete drawn (Just a empty MsgBox appears without text, just the "DEBUG" title).

What is going wrong?