QGLWidget::makecurrent(): GetDC() failed. Invalid Window handle

Question

Hello,

I have a requirement to get pictures saved off screen. I have used QGLwidget::grabframebuffer to get this done. While it works fine on MAC, it fails with an error "QGLWidget::makecurrent(): GetDC() failed. Invalid Window handle " on Windows 7. Only one opengl context gets created in the process. But i have observed that if I add QGLWidget to the Mainwindow, i am able to get the pictures saved. I need not do this on MAC to get the pictures. I am not sure what could have gone wrong.

thanks!!