If a user is submitting a form through my website – does the server side validation have to provide anything more than “error: invalid submission”?
If my client side validation is strong enough (and error reporting good and friendly), and if my server side validation is strong too – does the server side error response have to transmit any useful info to the submitter?
Server side validation is for protection, not guiding the user right?
Server-side validation is still needed for users with Javascript disabled.
You need to decide how much support you want to give them.
You should make sure that the errors do not reveal any implementation details.