CausesValidation in asp:MenuItem
Using Menu / MenuItems in a form for New, Update and Delete operations is more winningly than using Buttons, and it works fine too. However, there is an important difference between MenuItems and Buttons, the CausesValidation property is not available in MenuItems. This means you can't implement appealing client side validations using ShowMessageBox.
My suggestion: include the CausesValidation property in MenuItems, set the default value to false.