>When I try this:
>
>

>        TextBox TextBox1 = new TextBox();
>        this.Controls.Add(TextBox1);
>

>
>I get a page error "Control 'ctl02' of type 'TextBox' must be placed inside a form tag with runat=server. "
>
>Is there no way to do this in C# in the page_load? Or must I do it with tags?

Your form tag in your page need to be defined in an ASP.NET format instead of a regular HTML format. So, it is something like:

<form id="Form1" method="Post" runat="server" class=Form>