\This is the original that loads the contents of the first .printableArea.
\Changing the code to [1] instead of [0] gives the contents of the second .printableArea

<input type="button" align="centre" onclick="printDiv('printableArea')"
value="Print Page" />
<script>
function printDiv(divName) {
 var printContents = document.getElementsByClassName(divName)
 [0].innerHTML;
 var originalContents = document.body.innerHTML;

 document.body.innerHTML = printContents;

 window.print();

 document.body.innerHTML = originalContents;
 }
 </script>

\This also yields a result if I change to using an id instead of class.

<input type="button" align="centre" onclick="printDiv('printableArea')"
value="Print Page" />
<script>
function printDiv(divName) {
 var printContents = document.getElementById(divName).innerHTML;
 var originalContents = document.body.innerHTML;

 document.body.innerHTML = printContents;

 window.print();

 document.body.innerHTML = originalContents;
}
</script>