AppendItemValue Failing On A Date Type Object When Using Xpages

Hi
I have a complex page where I am trying to submit a date value to the backend document (a text value works) I always end up with a runtime error "[TypeError] Exception occurred calling method NotesDocument.appendItemValue(string, java.util.Date) null"
I have dummied up a simple piece of code to show what im doing and where the error is
I must be missing something but I just cant see it.
Oh don't think it make any difference but I'm using 8.5.2 with Extension Library installed
Thanks In Advance
Neil

Unexpected runtime error
The runtime has encountered an unexpected error.

Error source
Page Name:/test.xsp
Control Id: button1
Property: onclick


Exception
Error while executing JavaScript action expression
Script interpreter error, line=7, col=8: [TypeError] Exception occurred calling method NotesDocument.appendItemValue(string, java.util.Date) null

JavaScript code


   1: var db:NotesDatabase=database;
   2:   var fd = requestScope.ff_date.toString()
   3:   var fdate = new Date(fd);
   4:   requestScope.ff_date1 = fdate;
   5:   var rdoc:NotesDocument=db.createDocument();
   6:   rdoc.appendItemValue("Form","test");
   7:   rdoc.appendItemValue("test_date",requestScope.ff_date1);

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<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core">

	<xp:button value="Save Date" id="button1">
		<xp:eventHandler event="onclick" submit="true"
			refreshMode="complete">
			<xp:this.action><![CDATA[#{javascript:  var db:NotesDatabase=database;
  var fd = requestScope.ff_date.toString()
  var fdate = new Date(fd);
  requestScope.ff_date1 = fdate;
  var rdoc:NotesDocument=db.createDocument();
  rdoc.appendItemValue("Form","test");
  rdoc.appendItemValue("test_date",requestScope.ff_date1);}]]></xp:this.action>
		</xp:eventHandler></xp:button>
	<xp:br></xp:br>
	<xp:inputText id="inputText1" value="#{requestScope.ff_date}">
		<xp:dateTimeHelper id="dateTimeHelper1"></xp:dateTimeHelper>
		<xp:this.converter>
			<xp:convertDateTime type="date" dateStyle="full"></xp:convertDateTime>
		</xp:this.converter>
	</xp:inputText>
	<xp:br></xp:br>
	<xp:label value="#{javascript:requestScope.ff_date1}" id="label1"></xp:label></xp:view>

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