Unable to add new App Firewall Rule using REST API call to vCNS 5.1

I am trying to add some new App Firewall rules to vCNS 5.1

These are the following code. But I keep getting this error message "The remote server returned an error: (412) Precondition Failed.". Any help ?

TestRule2 is the new rule that i am trying to add.

Request Header has generationNumber added as If-Match

Request Body

POST https://vcns-ip/api/2.0/app/firewall/mycontextid/config

<?xml version="1.0" encoding="UTF-8"?>

<VshieldAppConfiguration>

  <firewallConfiguration contextId="datacenter-2" generationNumber="1394666438168" provisioned="true">

    <layer3FirewallRule id="0" precedence="none" disabled="false">

      <name>TestRule2</name>

      <action>allow</action>

      <logged>false</logged>

      <notes /><source>

      <address exclude="false" />

      <portInfo />

      </source>

    </layer3FirewallRule>

    <layer3FirewallRule id="1002" precedence="default" disabled="false">

      <name>Default Rule</name>

      <action>allow</action>

      <logged>false</logged>

      <notes />

    </layer3FirewallRule>

    <layer2FirewallRule id="1001" precedence="default" disabled="false">

      <name>Default Rule</name>

      <action>allow</action>

      <logged>false</logged>

      <notes />

    </layer2FirewallRule>

  </firewallConfiguration>

</VshieldAppConfiguration>