i've already be added the following lines to prevent caching, the contents is display within a iframe
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-Equiv="Cache-Control" Content="no-cache">
<meta http-Equiv="Pragma" Content="no-cache">
<meta http-Equiv="Expires" Content="0">
But it has no effect, any ideas?