DateTimePicker invalidate field

[Felix]

Hey,

im trying to have the same style to show the user that an input is invalid. Im using a RadTextBox, a RadNumericTextBox and a DateTimePicker with asp:CustomValidator each. For the two text boxes i can set

textbox.Invalid = true

but there is no such property in the DateTimePicker. I like the red border with the red exclamation mark in the text boxes and would like to use them for the DateTimePicker, too, but the only thing that works for me right now is to set an ErrorMessage for the Validator.

Do I fail to see how this works? Because there are forum threads asking for a way to not mark the field like I want to.

Greetings

Felix