Resolution:
No. The ErrorCode and Error Message properties of the business service can be used only for the errors encountered in the Adapter and the custom Business Service. The user can not explicitly set these parameters.

One could concatenate the error code and error message returned by the external application(or processing error in BW) into a single string, send the string as the reply to the siebel adapter. This reply string could be accessed from the EAI TIBCO HTTP Agent/EAI TIBCO Agent Adapter Business Service as property 'ReplyString'. In the Siebel application you could implement a logic to read the 'ReplyString' property and take necessary actions depending on the error code and error message extracted from the reply string.

In case of Request Response Invocation Service, is it possible to send the errors occuring in external application(RPC Server) to Siebel as an exception(error) instead of a propertyset through the custom Business Services?