syntax error correction please

This won't work, because you are writing asp control on the runtime to the browser, which won't be rendered. Instead, if you want to show a textbox dynamically, as it seems, you can use HTML textbox syntax, as given below:

Response.Write(<input type="textbox" id="dsde"  runat="server" />");

Hope this helps.

That's not really possible, by the means with which you are attempting to do it. Response.Write is processed on the server and so are the ASP.NET controls, there's no way to register text written to the page as a control by Response.Write.

Instaed you can use HTML controls or there are other options you can use for ASP.NET, such as the PlaceHolder control. If it is something that you need to show for some users and hide for others, you can use the Visible property of the textbox control, eg:
Code:
<asp:TextBox id="TextBox1" runat="server" Visible="False">

change your code as shown below :

Response.Write("" + "<asp:TextBox ID='dsde' runat='server'></asp:TextBox>")

Without asking why you'd want to do this and answering the question (such as it is) as asked, try:

Response.Write(@"<asp:textbox id=""dsde="" runat=""server"" />");