signing messages with a X509 certificate

Hi,
I want to sign a message with a x509 certificate, following this detailed description here: http://blog.thilinamb.com/2011/02/invok ... -with.html.
A screenshot of my configuration is attached.
No message signature is shown in SoapUI prior to sending the request:

<soapenv:Envelope xmlns:sam="http://www.example.com/sample" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Header><wsse:Security soapenv:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"/></soapenv:Header>
   <soapenv:Body>
      <sam:SampleProcessRequest>Test</sam:SampleProcessRequest>
   </soapenv:Body>
</soapenv:Envelope>

This is confirmed by the log at the receiving end where the message received is:

<soapenv:Envelope xmlns:sam="http://www.example.com/sample" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
 <soapenv:Header>
  <wsse:Security soapenv:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"/>
 </soapenv:Header>
 <soapenv:Body>
  <sam:SampleProcessRequest>Test</sam:SampleProcessRequest>
 </soapenv:Body>
</soapenv:Envelope>

The signature is obviously missing. I'm using SoapUI 5.0.
Has anybody got it working?
Thanks for any help you could provide.
Christian