Exceptions in DotNet

control gridview of type 'gridview' must be placed inside a form tag with runat=server

You are calling GridView.RenderControl(htmlTextWriter), hence the page raises an exception that a Server-Control was rendered outside of a Form.

You could avoid this execption by overriding VerifyRenderingInServerForm

public override void VerifyRenderingInServerForm(Control control)

{

  /* Confirms that an HtmlForm control is rendered for the specified ASP.NET

     server control at run time. */

}