To fix the issue with the error message we will need to copy the same file to a different location. Please replace the attached file in this location:
C:\Program Files\Common\Adobe\Installers\[Adobe Number]\Adobe Dreamweaver CS4\Configuration\Behaviors\Actions\WA Validation Toolkit\Apply Client Validations
(Make sure to have Dreamweaver closed)
In regard to your question about the client validation could you tell me the steps you took. Because i did a test and it seems that the required validation is firing up every time i click the submit button.