Capturing soap errors in PI

Dear Scn users,

I have a proxy->webservice scenario.

If there is something wrong while sending data to webservice(Ex:wrong username)there will be error which will be displayed as"invalid username" if we test using soap UI.

But in PI it will shown only as http 500 error,How to capture this error in PI like soap UI.

In PI also it should show as "Invalid Username".

How to achieve this.