Automatic Download

I am using the following case to automatically download when a user clicks on a link.  The code works good for all files being downloaded that are smaller than about 4M.  Any 4M file and larger seems to generate a page cannont be displayed error.  Possibly some type of memory error/allocation I'm not sure...  How can I fix this, or is there an entirely different way to be going about solving my problem.  

      case "download"
                  dim filedir
                  filedir = request.querystring("dir")
                  
                  Response.Buffer = True
                  strFileName= "00000001.tif"
                  strFilePath=server.mappath(filedir&"\"&strFileName)
'                  strFilePath= "C:\Onetrac\Programs\intranet site\Oldstone\" & filedir &"\"
                  response.write(strFilePath)
                  set fso=createobject("scripting.filesystemobject")
                  set f=fso.getfile(strFilePath)
                  strFileSize = f.size
                  set f=nothing: set fso=nothing
                  Const adTypeBinary = 1
                  Response.Clear
                  Set objStream = Server.CreateObject("ADODB.Stream")
                  objStream.Open
                  objStream.Type = adTypeBinary
                  objStream.LoadFromFile strFilePath
                  strFileType = "image/tif" ' change to the correct content type for your file
                  Response.AddHeader "Content-Disposition", "attachment; filename=" & filedir & ".tif"
                  Response.AddHeader "Content-Length", strFileSize
                  Response.Charset = "UTF-8"
                  Response.ContentType = strFileType
                  Response.BinaryWrite objStream.Read
                  Response.Flush
                  objStream.Close
                  Set objStream = Nothing