Unable to download file which is more than 2 KB in Windows 7 & IIS 7.5

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Windows

Win7

In my machine I have installed Windows 7 along with IIS 7.5.
I have created virtual path as "TestAsp" ("C:\inetpub\wwwroot\TestAsp").
I am unable to download a file which more than 2 KB

I have used following code in a asp file to download a file

<%
'Set the content type to the specific type that you are sending.

strFilePath = "C:\inetpub\wwwroot\TestAsp\Bin\Test1big.txt"
'Note : File size of 'Test1Big.txt' is morethan 2 KB

Set fso = CreateObject("Scripting.FileSystemObject")
if fso.FileExists(strFilePath) Then
	set file = fso.GetFile(strFilePath)	
		
	Response.buffer = TRUE  
	Response.Expires = 0
	Response.Clear
	Response.ContentType = "application/octet-stream"
	Response.AddHeader "Document", fso.GetFileName(strFilePath)
	Response.AddHeader "Content-Length", file.size	
	Response.AddHeader "Content-Disposition", "attachment; FileName=" &
		fso.GetFileName(strFilePath)
	Const adTypeBinary = 1
	Set objStream = Server.CreateObject("ADODB.Stream")
	objStream.Open
	objStream.Type = adTypeBinary
	objStream.LoadFromFile strFilePath
	Response.BinaryWrite objStream.Read
	objStream.Close
	Set objStream = Nothing
Else
	Response.Write("File " & strFilePath & " does not exist.")
End if
Set fso = Nothing
%>

During my further investigation I have found that the following line in the asp page was causing the problem
"Response.AddHeader "Content-Length", file.size"
Once I comment the above line from the asp page I was able to download a file which is more than 2 KB.

I want to download a file without commneting above said line.

Can you help me on this

Thx in advance

Zulfiqar