While I am Downloading ,One Dialogbox will open.When user will be saving file name...that time I want to restrict user to change the file name ..I have written code below for downloading file.

Dim fs As System.IO.FileStream = Nothing
fs = File.Open(Server.MapPath("TextFiles/Branch/" + filenam + ".txt"), System.IO.FileMode.Open)
Dim btFile(fs.Length) As Byte
fs.Read(btFile, 0, fs.Length)
fs.Close()
With Response
.AddHeader("Content-disposition", "attachment;filename=" & filenam)
.ContentType = "application/octet-stream"
.BinaryWrite(btFile)
.End()
End With


With Regards,
mishrap