Hello Dominique,
The value entered in a RadNumericTextbox control is not submitted if it is out if the range specified by MinValue and MaxValue properties. This is the way the control was built to work. In order to achieve the behavior you describe you could use different approaches depending on your current requirements.
You could add a RequiredFieldValidator for the RadNumericTextBox. This way postback will be prevented if the value entered is not between MinValue and MaxValue. Check the following code snippet for illustration.
Another possible approach is to use a CustomValidator control and handle the validation manually. You could add custom client- and server-side validation methods.
On a side note, the version of the controls you are using is rather old. It is always recommended to use the latest version of our controls as it includes different improvements and new features.
Regards,
Viktor Tachev
Telerik
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