Error Consuming Web Service:Unsupported xstream found:("HTTP Code 200:OK")

I am trying to consume a web service from an Outbound Proxy. I am getting the following error message:-

Unsupported xstream found: ("HTTP Code 200 : OK")

This is a System Exception generated while I call the Outbound Proxy.

Kindly let me know what could be the issue.

An early reply will be highly appreciated as I am getting this issue in my Production Server.