VALIDATOR Assistant
With a form in the open document, put your cursor where you want the Error Message to appear. Then, running the ASP.Net Validator Assistant will 'GRAB' all the field names from the form and puts them in a pull-down menu on the VALIDATOR Assistant dialog box.

Validator Assistant

All you must do then, is to assign an ID to the control, choose whether or not you need a Regular Expression Validator or a Required Field Validator, choose the Form Field you want to validate, and create your Error Message that you want displayed. Once you click the 'Apply' button, the code is inserted where your left your cursor.