Opportunity End date to trigger Action

Hello,

I have a requirement to Start an Action 6 weeks before the end date of the Opportunity. I have set up a Date rule and assigned it to a Date profile which is in turn assigned to the action. When I try to test it I get the message 'Start condition is not fullfilled'. I know Action is set up correctly as I can Start it via a Status change by changing the 'Start Condition' but it doesn't seem to work when I use the Date Rule.

Here is the XML Date Rule for 6 weeks before Opportunity End date.

<?xml version="1.0"?>
<SAPTimeRule>
<TimeRuleTree>
<!-- Begin of Rule Tree -->
<ruleline>
<!-- Begin of new LINE -->
<AssignTimeExp displaytype="AssignTime">
<!-- Assign time -->
<VarTimeExp displayType="VarTime"
name="RESULT"
position='B'>
<!-- Variable: Time -->
</VarTimeExp>
<MoveTimeExp displaytype="MoveTime" direction="-">
<!-- Move -->
<VarTimeExp displayType="VarTime"
name="VALIDTO"
position="B">
<!-- Variable: Time -->
</VarTimeExp>
<ConstDuraExp displaytype="ConstDura"
duration="6" timeunit="WEEK">
<!-- Constant Duration -->
<VarObjectExp displaytype="VarObject"
name="SYSTEM"/>
<!-- Variable: Timeobject -->
</ConstDuraExp>
</MoveTimeExp>
</AssignTimeExp>
</ruleline>
</TimeRuleTree>
</SAPTimeRule>

I'm not sure if the 'VALIDTO' is the correct name for the checking the Opportunity End Date.

Regards

Chan