As a work-around, one of my colleagues has suggested using a formatted Content Block (or a styled Read Only Text) combined with a Visibility Expression to produce your validation message. You can use the expression on one or more buttons to modify the value of a variable, and use that value as a flag to control the visibility of the message. Since Visibility Expressions are evaluated each time the form loads or posts back - whereas a Validator Expression will only react to postbacks on the same page - this would be a more reliable way of achieving your aim here. The added benefit of using a content block is you can apply in-line styling and deploy re-usable assets to have consistent validation messages in more than one location. Let me know if any of this is unclear. Kind regards.