Plugins: Validation Reflection and Client-Side Val

Has anyone used this plugin?

Yes, me... but I'm the author. Are you using the latest version? There
was a small error in a previous version that didn't load the
locale-specific validation functions.

I have installed both validation_reflection and
client_side_validation, added class="validated" to my form,
Form.Validator.installForAllValidatedForms( ); in application.js,
.invalid { ... } in stylesheet.
In IE 6, when I load the page I get 'object doesn't support this
property ...'. In FF no error. But in both I can submit the form with
erros, no javascript alert or smt...

As far as my own experience goes, client-side validation works in
Firefox, IE6, and Konqueror. The fault I mentioned above may well be
what's causing the problems you're seeing.