In original mode, which acknowledgment code is returned by the receiver if the originating message has an invalid value for message type, version ID, or processing control ID?

The acknowledgment code returned by the receiver in response to an originating message that has an invalid value for message type, version ID, or processing control ID is AR, which stands for Application Reject.

This code specifically indicates that the message cannot be processed due to issues with the data being sent. When the receiving application identifies that there is something fundamentally wrong with the incoming message—such as an invalid message type or improper versioning—it signifies that it cannot accept the message for processing due to its inability to adhere to expected standards or protocols.

The significance of the AR acknowledgment is that it lets the sender know not only that the message was received, but also that it failed validation checks regarding its format or content. This informs the sender that corrective action is necessary before resending the message.

Other acknowledgment codes serve different purposes. For example, the RR code is used when a message is rejected due to specifically business logic issues rather than structural issues like those indicated by AR. AA indicates that the message was accepted without issues, while AE indicates an error that occurred during processing, not necessarily relating to the invalid formatting or headers that pertain to AR.