Use the CausesValidation property to determine whether validation is performed on both the client and the server when a CheckBox control is selected. Page validation determines whether the input controls that are associated with a validation control on the page all pass the validation rules as specified by the validation control.
By default, clicking a CheckBox control does not cause page validation. To perform page validation when the CheckBox control is clicked, set the CausesValidation property to true.
When the value of the CausesValidation property is set to true, you can also use the ValidationGroup property to specify the name of the validation group for which the CheckBox control causes validation.