Crystal Reports :: Viewer Toolbar Button Control - Microsoft JScript Runtime Error

I am working with crystal reports. I created a button on crystal report viewer toolbar using the following code protected void Page_Init(object sender,

EventArgs e)
{
Control ts = CrystalReportViewer1.Controls[2];
if (ts.ToString().Contains("ViewerToolbar"))
{
ImageButton BtnExport =
new
ImageButton();
BtnExport.ID = "BtnExport";
BtnExport.ImageUrl = "images/pdf.png";
BtnExport.Click += BtnExport_Click;
ts.Controls.Add(BtnExport);
}
UpdatePanel UpdatePanel1 =
new
UpdatePanel
();
System.Web.UI PostBackTrigger trigger =
new System.Web.UI.PostBackTrigger ();
trigger.ControlID = "BtnExport";
UpdatePanel1.Triggers.Add(trigger);
}

My problem is whenever I click the button to export the report, it shows an error like below: Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.
Details: Error parsing near .....