"Cannot get inner content of frm1 because the contents are not literal." error in building a dynamic form within other HTML

Question

Hi, 
I am trying to build an aspx form dynamically but I have to user some HTML tags among controls. I am getting the error "Cannot get inner content of frm1 because the contents are not literal." in my 
oForm.InnerHtml += "</fieldset>";
instruction. If I put it before adding the text and button controls to the form the error is gone. What am I doing wrong, if I want the controls to be inside a <fieldset> ... </fieldset> tag?
public void LoadForm()
HtmlForm oForm = new HtmlForm();
oForm.ID = "frm1";
oForm.Action = "";
oForm.InnerHtml += "<fieldset>";
oForm.InnerHtml += "<legend> ### TITALO ### </legend>";
HtmlInputText oText = new HtmlInputText();
oText.ID = "txt";
HtmlInputSubmit oSubmit = new HtmlInputSubmit();
oSubmit.ID = "btn";
oSubmit.Value = "submit";
oForm.Controls.Add(oText);
oForm.Controls.Add(oSubmit);
oForm.InnerHtml += "</fieldset>";
main.Controls.Add(oForm);
Thanks, regards. 
Bruno

Answer 1

According to articles (e.g.
http://forums.asp.net/t/939432.aspx?Panel+GroupingText), in order to include a
<fieldset>, you can use a Panel control having GroupingText
attribute. Therefore, instead of dealing with InnerHtml, try this:
var panel = new Panel { GroupingText = "### TITALO ###" };
panel.Controls.Add(oText);
panel.Controls.Add(oSubmit);
oForm.Controls.Add(panel);
main.Controls.Add(oForm);