It might be you have used Forms Authentication in your application. Put another Web.config file in your Images folder and remove the Authentication from that file.

Remove the break; statement from the For each loop.

Try following code:

protected override void OnInit(EventArgs e)
{
base.OnInit(e);
LinkButton lnk = new LinkButton();
lnk.Text = "My Link";
lnk.Click += new EventHandler(lnk_Click);
plcHld.Controls.Add(lnk);
}

    void lnk\_Click(object sender, EventArgs e)
    {
        lblMessage.Text = "Link Clicked";
    }

As you said the Link button is created Dynamically, you have to create it Every Time when the page is post back, also create it in the Init event of the user control.

Following code should solve your problem:

Response.Clear();
Response.ContentType = "text/plain";
Response.WriteFile("D:\\ADIB\\OutputXML.xml");
Response.Flush();

Add follwoing style to get scroll bar:

style="overflow: auto"

You can use Required field validator control... Enjoy coding....