Problem with Literal Control on web form

I have on my page some regular html code as well as an asp Literal control.
<center>
<br />
<h1>Thank You!!!!!</h1>
<asp:Literal ID="tk" Text="<h1>Thank You!</h1>" runat="server"></asp:Literal>
</center>

Then in my *.cs file I have a loop to go through the controls and make set the visible property of
some to false and others to true.


private void ControlLoop()
{
Control form = Master.FindControl("form1");
Control main = form.FindControl("MainContentPlaceHolder");
Control side = form.FindControl("LeftSideContentPlaceHolder");

foreach (System.Web.UI.Control ctrl in main.Controls)
{

if (ctrl.G ...