Can't start file download from server side using .aspx file in IE7

Hi all,
This below code i have used in my aspx page for file download.
 
Response.AppendHeader("content-disposition", "attachment; filename=\"" + emailAttachment.FileName + "\";");
Response.ContentType = "application/octet-stream";
Response.OutputStream.Write(emailAttachment.Data, 0, emailAttachment.Data.Length);
Response.End();
 
This block of code display Download file Dialog for Open or Save the attached file.It’s working fine in Mozila Firefox and IE8 but doesn’t display Download file Dialog box in IE 7Please help me with this
 
Thanks,Yogesh
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