delegation, problem at step 2.7

[Steven Carmody]

this is the almost final step:

> Portlet Forwards <samlp:Response> to Web Service Provider

I've constructed the SOAP msg described in the example attached to step 2.7:

https://spaces.internet2.edu/display/ShibuPortal/Solution+Proposal

I've POSTing it to the responseConsumerURL url contained in the backend 
service's response to the initial ECP request.

However, I'm getting this back from the backend service:

<p>Please include the following message in any email:</p>
<p class="error">opensaml&#58;&#58;BindingException at 
(http&#58;//stc-test3.cis.brown.edu/Shibboleth.sso/SAML2/ECP)</p>

<p>Invalid content type for PAOS message.</p>

Am I POSTing to the correct url ?

... and what should I set the content type to ?

Thanks!