Error message when trying to send message thru private localhost q

I have installed WinFX Beta 2 of on Windows XP SP2.
I have created a private non-transactional message queue.
My client application gives me the following error message when I try to
send a message (e.g. base.InnerProxy.FunctionCall(data);
"There was an error sending to the queue: No internal Message Queuing
certificate exists for the user. (-1072824273, 0xc00e002f)".
I have setup my binding as follows:
<netMsmqBinding>
<binding
name="netMsmqBinding_IProcessTestData"
exactlyOnce="false" >
<security>
<message clientCredentialType="None" />
</security>
</binding>
</netMsmqBinding>

Does anyone have an idea what I might be doing wrong?
Thanks.