I have a date in a text box that controlled its validation with "CompareValidator"
<asp:CompareValidator ID="Validator" runat="server" ControlToValidate="txtFecha" CultureInvariantValues="true" ErrorMessage="Fecha incorrecta" SetFocusOnError="DataTypeCheck" Text="" Type="Date"></asp:CompareValidator>
When the date is incorrect, the message in red is displayed as "Incorrect date" when changing the focus and going to another text box to fill in. So all right.
The problem I have is when I want to move to another form by pressing a "next" button since I want to show me a mandatory field message if no date has been entered. For this I look if the text box txtFecha.Text == "" and if it is so filling CompareValidator.Text = "Campo obligatorio" but does not show me the message.