I develop a program and I have 10 backups of it. I added some lines to it and when I compiled the project and now it has the following error:

C:\Qt\Qt5.0.1\5.0.1\mingw47_32\include\QtWidgets\qtabwidget.h:173: error: 'QTabWidget::QTabWidget(const QTabWidget&)' is private

the error is from * line

namespace Ui {
  class ContentControl;
}

class ContentControl : public QTabWidget // * from this line
{
    Q_OBJECT

public:
.
.
.
}

All backups have this error now. Any idea why? I re-installed Qt but the problem is still present.