我的主程序Program.cs里面有

        public struct Message
        {
            private readonly string userName;
            private readonly string content;
            private readonly DateTime postDate;

            public Message(string userName, string content)
            {
                this.userName = userName;
                this.content = content;
                this.postDate = DateTime.Now;
            }

            public Message(string content) : this("System", content) { }

            public string UserName
            {
                get { return userName; }
            }

            public string Content
            {
                get { return content; }
            }

            public DateTime PostDate
            {
                get { return postDate; }
            }

            public override string ToString()
            {
                return String.Format("{0}[{1}]：\r\n{2}\r\n", userName, postDate, content);
            }
        }

然后我在Form2.cs里面调用
            // 发送消息
            private void btnSend_Click(object sender, EventArgs e)
            {
                if (String.IsNullOrEmpty(txtContent.Text))
                {
                    MessageBox.Show("请输入内容！");
                    txtContent.Clear();
                    txtContent.Focus();
                    return;
                }
                Message msg = new Message(userName, txtMessage.Text);//这里就出错了
                if (talker.SendMessage(msg))
                {

错误报告：E:\ProgramFiles\Projects\Bruce\Bruce\Form2.cs(94,31): 错误 CS0143: 类型“System.Windows.Forms.Message”未定义构造函数


请问是为什么？我正在用socket编聊天程序。