return status and/or fault ?

hi,

Normally when there is a problem the NS will return fault messages (as by the SOAP standard). But what I also encountered is that even if i dont have fault the operation can still be failing f.e.

{
'status' => {
'statusDetail' => {
  'message' => 'A record with the same unique signatures already exists. You must enter unique signatures for each record you create.',
  'code' => 'USER_ERROR'
   }
}
};

see no fault, but still error..
My question is, how can I figure out when I have error in these cases.. ?
i.e. how to distinguish them from successful execution, so I can add the required error handling code ?