A quick search of Google for "validate checkbox", you would find that one of the results is: and this explains how validations work.
Here's a page that validates a checkbox: I would like to validate that a Checkbox is checked on the client-side.
If you then click the button when the checkbox is checked, you should see no errors.
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Indeed, the built-in validator controls cannot validate the checkbox.
You will have to use the custom validator to do this or write your own client side validation.
Validation server controls are a series of controls that help you validate the data that the user enters into the other controls that are provided with ASP. They determine whether the form can be processed based upon the rules that you define in the validation server controls.