The CreateUserWizard.SendMailError event is raised when there is a problem using the SMTP mail provider to send e-mail to the e-mail address provided by the new user. The most common reason to raise this event is when the <smtpMail> section of the Web.config file is incorrect.
The default CreateUserWizard.SendMailError event handler does not catch or handle the SMTP error from the e-mail system. Your CreateUserWizard.SendMailError event handler must set the SendMailErrorEventArgs.Handled property of the System.Web.UI.WebControls.SendMailErrorEventArgs object to true in order to stop the error from appearing to the Web site user.
For more information about handling events, see Consuming Events.