ASP uploading/transferring images

I have an ASP web service, that allows to various users to put some data in a database and to upload some images. Since the users have different web sites, the web service uploads the image in a first directory in its own space, then calls an ASP web page located in the user's domain passing it the path to the image (correctly stored) as follows:

MResponseBackAsp(Session("Dominio") & "trasferisci.asp?nomefile=" & Session.SessionID & "-" & name)

So, here it comes the trouble, I receive the following message:

Microsoft VBScript runtime error '800a0005' 
Invalid procedure call or argument 
/trasferisci.asp, line 28 Si è verificato un errore nel salvataggio dell'immagine

The code relative to that line is commented:

<%  
nomeFile = Request("nomefile")

Dim lStato
Dim objHTTP
Dim strDataIn
'Randomize()

Set objHTTP = CreateObject("Microsoft.XMLHTTP") 
objHTTP.Open "GET", "http://URL/" & nomeFile, False 
objHTTP.Send 
lStato= objHTTP.Status
strDataIn= objHTTP.ResponseBody 'Binario 
Set objHTTP = Nothing 

If (lStato<>200) Or (Err.Number<>0) Then 
  problema = "Errore " & lStato & " o " & Err.Description & "."
End If

newNomeFile = right(nomeFile,len(nomeFile)-instr(nomeFile,"-"))
fileDaSalvare = Server.mapPath(Application("news_immagini") & newNomeFile)

Set objFSO = Server.CreateObject("Scripting.FileSystemObject")
If objFSO.FileExists(fileDaSalvare) Then objFSO.DeleteFile(fileDaSalvare)
Set objFl = objFSO.CreateTextFile(fileDaSalvare, true)
objFl.Write BinaryToString(strDataIn)
objFl.Close()
Set objFl = Nothing
Set objFSO = Nothing

Function BinaryToString(Binary) 
  dim c1, c2, c3, p1, p2, p3 
  Dim L 
  c1 = 1 :  c2 = 1 : c3 = 1 
  L = LenB(Binary) 

  Do While c1<=L 
    p3 = p3 & Chr(AscB(MidB(Binary,c1,1))) 
    c1 = c1 + 1 : c3 = c3 + 1 
    if c3>300 then 
      p2 = p2 & p3 
      p3 = "" 
      c3 = 1 
      c2 = c2 + 1 
      if c2>200 then 
        p1 = p1 & p2 
        p2 = "" 
        c2 = 1 
      End If 
    End If 
  Loop 
  BinaryToString = p1 & p2 & p3 
End Function

Response.write "salvato"
%>

But the best parts come now: 1) If we call trasferisci.asp manually it works; 2) If we refresh the global.asa then it works again for a while

I read somewhere that there could be some problems whit image upload, where is the problem? Suggestions?

Thank you all folks.

PS (edit): I've posted this question here because we think that the problems are into the System, not into the code. I apologyze if it is not.