Thanks to Doug and Jeff for their input on the Acknowledgment/RefToMessageId question...I guess for now we stick with the "Acknowledgment/RefToMessageId matches MessageData/RefToMessageId...usually." approach ;-) My other concern is in regard to CPA practicalities when sending combined (hybrid) MSH Signal Ack and Business Message packages. Suppose such a hybrid is sent SyncReply to an Action Binding that is configured with "isNonRepudiationRequired = true". However the sync DeliveryChannel being used specifies "ackSignatureRequested = never". So there is potentially a conflict as to whether the MSH Ack/Business Response hybrid message would be signed (also for the reverse..isNonRepudiatedRequired = false, ackSignatureRequested = always). Does this conflict indicate that the CPA instance is "invalid"? Or is the signing of a hybrid message determined by OR logic. ie if the MSH signal OR the Business Message requested signing then then hybrid message package gets signed...? Thanks again, Dave Elliot XML Global Technologies