Problem In Viewing MHTML Report When It Is Exported

Hi, I am facing a different problem when MHTML report is exported, this happens in alternatve requests, but when I save the file report is proper.The only problem is when I click on Open button , it pops another dialouge with

Name: wbk3E.tmp
Type: HTML DOcument
From :mhtml:http://localhost/riq/web/UI/RunReports.aspx

wbk3E.tmp file is not displaying any report data, I am not getting what happens when I click on Open button..The same code is working on first request and its alternative requests fails to show the report...I don't have any problem with CSV and XML exports.

Please suggest me what is the problem in opening the report on Even open clicks. The below lines of code that renders the report.

try
{
Response.Clear();
Response.ClearContent();
Response.ClearHeaders();
switch (_format)
{
case "MHTML":
Response.ContentType = "text/mhtml";
Response.AddHeader("Content-disposition", "attachment;filename=output.mhtml");
break;
}
Response.OutputStream.Write(m_bytes, 0, m_bytes.Length);
Response.OutputStream.Flush();
Response.OutputStream.Close();
Response.Flush();
Response.Close();
Response.End();