解决方法
您可以根据验证逻辑在
OnServerValidate方法中设置错误消息：
protected void customValidator1_Validate(object sender,ServerValidateEventArgs e)
{
if (e.Value.Length < 5)
{
e.IsValid = true;
}
else
{
customValidator1.ErrorMessage = "Length must be less than 5.";
e.IsValid = false;
}
}
