3.1.4.2 Failure Cases
WDS Server MUST return a failure status for the RPC call if it encounters any failure before passing the request to a Service Provider, or after the reply packet has been handed to WDS Server by a Service Provider.
Service Providers SHOULD report failures by instructing the WDS Server to return the appropriate failure code for the RPC call.
Service Providers MAY construct a reply packet and set the failure error code in the Operation Header (section 2.2.1.2). In this case, the RPC call succeeds, but the OpCode-ErrorCode field in the Operation Header MUST contain the appropriate error code.<2>