UserControl with a TextBox inside: how to fire the ErrorTemplate of the TextBox instead of the UserControl's one.

I created a UserControl wich has a TextBox inside. The value of the "Text" property of che UserControl (bound, of course, with the TextBox) is validated, but when it has errors I see the ErrorTemplate of che UserContol instead of the ErrorTemplate of the TextBox.

How can I do to "notify" the validation error to the TextBox, so I can see its ErrorTemplate?

Hope you can help me, I'm going mad with this...

Francesco