So, I handle OnClosing for a Form, and check all UserControls, belonging to the Form, for some state. If the state is not "right", I set e.Cancel to true. Ok... But how I can reach all UserControls belonging to the Form if I have nested containers like TabPages and Panels?

You can handle the KeyDown event and check if the character was a numeric or not. If not you should set e.SuppressKeyPress to true. Regards:rose:

And what does it mean???