How to: Add and Configure a ValidationSummary Control
Use the ValidationSummary control to display a list of validation errors that occurred when a form was submitted. This control lists all the error messages generated by the other validation controls on the form. The ValidationSummary control obtains the error message strings from the ErrorMessage properties of the validation controls whose tests failed.
To display a summary of error messages
In the Properties window, set the FormToValidate property to the ID of the form for which you want to summarize error messages.
Optionally, type header text to precede the error messages in the HeaderText property.
Optionally, enter text for the back link in the BackLabel property.
The ValidationSummary control displays this link so that users can return to the form on which the error occurred and reenter data.