I got "Form control does not have ControlMode set" error
message when adding my custom web part in a subsite in MOSS 2007,
not sure what is wrong with my code, here's a code nippet of my web
part:

protected override void CreateChildControls()
{
button = new Button();
button.Text = "Search Employee";
button.Click += new EventHandler(button_Click);
Controls.Add(button);

ssnField = new TextField();
ssnField.ControlMode = SPControlMode.New;
Controls.Add(ssnField);

searchCriteriaLabel = new Label();
searchCriteriaLabel.Text = "Search Criteria";
Controls.Add(searchCriteriaLabel);

ssnLabel = new Label();
ssnLabel.Text = "Social Security Number: ";
Controls.Add(ssnLabel);
}

//Render web part to the web browser
protected override void RenderContents(HtmlTextWriter writer)
{
//Display data
writer.Write("<table border=\"0\" width=\"100%\">");

writer.Write("<tr><td>");
searchCriteriaLabel.RenderControl(writer);
writer.Write("</td></tr>");

writer.Write("<tr><td>");
ssnLabel.RenderControl(writer);
writer.Write("</td></tr>");

writer.Write("<tr><td>");
ssnField.RenderControl(writer);
writer.Write("</td></tr>");

writer.Write("<tr><td>");
writer.Write("</td></tr>");

writer.Write("<tr><td>");
button.RenderControl(writer);
writer.Write("</td></tr>");

writer.Write("</table>");
}