Which version of JBoss AS is this? What does your https server configuration look like?
We're using JBoss EAP 5.0.
Sadly we don't have access to the third party's https server config. Do you think their config could have a bearing on the issue?
I'm going to close this issue. Although I am still getting the error message, it turns out I can still talk to the web service. There were other bugs in the code stopping me from realising that.