I have the following validator on a textbox inside a modal dialog box.
<asp:RequiredFieldValidator runat = "server"
ErrorMessage = "Role name can not be empty."
ControlToValidate = "tbxRoleName" />
It works like it should, except that the validation triggers on every other buttons OnClick handler on the aspx-page too. Since the dialog is invisible it looks like buttons just dont work on the page. My workaround is to add CausesValidation = "false" on all buttons on the page. But it is a very bad solution and I think there should be a smarter way.