创建控件时出错，-LoginCtrl 实例方法的委托不能具有空this

Question

我在解决方案管理器里创建一个web自定义控件，已经创建好了编译成功已经在工具箱中找到该控件，但拖放到aspx 页面中是就出现上面的错误----创建控件时出错，-LoginCtrl  实例方法的委托不能具有空this
这是什么问题
    [DefaultProperty("BackColor")]
    [ToolboxData("<{0}:LoginCtrl runat=server></{0}:LoginCtrl>")]
    public class LoginCtrl : WebControl
    {
        private Color _fontColor = Color.Black;
        private Color _backColor = Color.White;        private Label lbUserName = new Label();
        private Label lbPassWord = new Label();
        private TextBox txtUserName = new TextBox();
        private TextBox txtPassWord = new TextBox();
        private Button submitButton = new Button();
        private Button clearButton = new Button();
        private System.Web.UI.WebControls.Panel pnlFrame = new System.Web.UI.WebControls.Panel();        public EventHandler SubmitOnClick;
        public EventHandler ClearOnClick;        public LoginCtrl()
        {
            this.lbUserName.Text = "用户名:";
            this.lbPassWord.Text = "密码：";
            this.txtPassWord.TextMode = TextBoxMode.Password;
            this.pnlFrame.Width = 240;
            this.pnlFrame.Height = 120;
            this.pnlFrame.BackColor = Color.Empty;
            submitButton.Text = "确定";
            submitButton.Click += new EventHandler(this.SubmitOnClick);
            clearButton.Text = "重置";
            clearButton.Click += new EventHandler(this.ClearOnClick);            this.Controls.Add(this.submitButton);
            this.Controls.Add(this.clearButton);
            this.Controls.Add(this.txtUserName);
            this.Controls.Add(this.txtPassWord);
            this.Controls.Add(this.lbUserName);
            this.Controls.Add(this.lbPassWord);
            this.Controls.Add(this.pnlFrame);         }
        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Color ForeColor
        {
            get
            {
                return this._fontColor;
            }
            set
            {
                this._fontColor = value;
            }
        }        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Color BackColor
        {
            get
            {
                return this._backColor;
            }
            set
            {
                this._backColor = value;
            }
        }        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public string UserName
        {
            get
            { return this.txtUserName.Text; }            set
            { this.txtUserName.Text = value; }
        }        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public string PassWord
        {
            get
            { return this.txtPassWord.Text; }            set
            { this.txtPassWord.Text = value; }
        }        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Unit Width
        {
            get
            {
                return this.pnlFrame.Width;
            }
            set
            {
                this.pnlFrame.Width = value;
            }
        }         [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Unit Height
        {
            get
            {
                return this.pnlFrame.Height;
            }
            set
            {
               this.pnlFrame.Height = value;
            }
        }         [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Color BorderColor
        {
            get
            {
                return this.pnlFrame.BorderColor;
            }
            set
            {
                this.pnlFrame.BorderColor = value;
            }
        }
         [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override BorderStyle BorderStyle
        {
            get
            {
                return this.pnlFrame.BorderStyle;
            }
            set
            {
                this.pnlFrame.BorderStyle = value;
            }
        }
        
        [Bindable(false)]
        [Category("Appearance")]
        [DefaultValue("")]
        public override Unit BorderWidth
        {
            get
            {
                return this.pnlFrame.BorderWidth;
            }
            set
            {
                this.pnlFrame.BorderWidth = value;
            }
        }        protected override void Render(HtmlTextWriter output)
        {
            this.pnlFrame.RenderBeginTag(output);            output.AddAttribute(HtmlTextWriterAttribute.Border, "0");
            output.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "0");
            output.AddAttribute(HtmlTextWriterAttribute.Cellspacing, "0");
            output.AddAttribute(System.Web.UI.HtmlTextWriterAttribute.Width, "100%");
            output.AddAttribute(System.Web.UI.HtmlTextWriterAttribute.Height, "100%");
            output.AddAttribute(HtmlTextWriterAttribute.Bgcolor,this._backColor.Name);
            output.RenderBeginTag(HtmlTextWriterTag.Table);
            output.RenderBeginTag(HtmlTextWriterTag.Tr);
            output.RenderBeginTag(HtmlTextWriterTag.Td);            this.lbUserName.ForeColor = this._fontColor;
            this.lbUserName.RenderControl(output);
            output.RenderEndTag();
            output.RenderBeginTag(HtmlTextWriterTag.Td);            this.txtUserName.RenderControl(output);
            output.RenderEndTag();
            output.RenderBeginTag(HtmlTextWriterTag.Tr);
            output.RenderBeginTag(HtmlTextWriterTag.Td);            this.lbPassWord.ForeColor = this._fontColor;
            this.lbPassWord.RenderControl(output);
            output.RenderEndTag();
            output.RenderBeginTag(HtmlTextWriterTag.Td);            this.txtPassWord.RenderControl(output);
            output.RenderEndTag();
            output.RenderEndTag();
            output.RenderBeginTag(HtmlTextWriterTag.Tr);
            output.AddAttribute(HtmlTextWriterAttribute.Align, "right");
            output.RenderBeginTag(HtmlTextWriterTag.Td);
            //在表格中添加Button控件
            this.submitButton.RenderControl(output);
            output.RenderEndTag();
            output.AddAttribute(HtmlTextWriterAttribute.Align, "center");
            output.RenderBeginTag(HtmlTextWriterTag.Td);
            //在表格中添加Button控件
            this.clearButton.RenderControl(output);
            output.RenderEndTag();
            output.RenderEndTag();            output.RenderEndTag();            this.pnlFrame.RenderEndTag(output);        }        private void Submit_Click(object sender, EventArgs e)
        {
            EventArgs e1 = new EventArgs();
            if (this.SubmitOnClick != null)
                this.SubmitOnClick(this.submitButton, e1);
        }
        private void CleaBtn_Click(object sender, EventArgs e)
        {
            this.txtPassWord.Text = "";
            this.txtUserName.Text = "";
            EventArgs e1 = new EventArgs();
            if (this.ClearOnClick != null)
                this.ClearOnClick(this.clearButton, e1);
        }