Using UserFields and Date Fields in Web Parts

[lday86]

Hi, I am creating a web part for Microsoft SharePoint and i need to add two controls, a userfield (to allow a user to be selected) and a date picker field. So far i have the following code:

protected override void CreateChildControls()
{
btnSubmit = new Button();
btnSubmit.Text = "Add to list";
btnSubmit.Click += new EventHandler(btnSubmit_Click);
Controls.Add(btnSubmit);

        txtTitle = new TextBox();
        Controls.Add(txtTitle);

        dateDueDate = new DateTimeControl();
        Controls.Add(dateDueDate);

        userAssignedTo = new UserField();
        Controls.Add(userAssignedTo);

        base.CreateChildControls();
    }


    protected override void RenderContents(HtmlTextWriter writer)
    {
        //RENDER CONTENTS
        btnSubmit.RenderControl(writer);
        writer.Write("<br />");
        txtTitle.RenderControl(writer);
        writer.Write("<br />");
        dateDueDate.RenderControl(writer);
        writer.Write("<br />");
        userAssignedTo.RenderControl(writer);
        writer.Write("<br /><br />");

However, the UserField and DateTimecontrol are causing the web part not to render. I am not sure if i am using the correct field types or adding them correctly. Any help would be great, Thanks in advance