In order to help us better help you, it would be best to provide all the information on what you want to do in a single thread, so we can have a better overall picture of what you are trying to do.
ANT is not an asynchronous protocol - the basis of its operation is for a master to transmit periodically and a slave to synchronize with its transmissions. If you haven't yet, it would be highly recommended to have a look at the following ANT presentation, which would give you a better understanding of the basic operation of the protocol
http://www.youtube.com/view_play_list?p=A4AA10B39DB19291
Sections 1 - 5 of the ANT Message Protocol and Usage document provide an overview of the main features and functionality of the protocol, and are an essential resource for understanding ANT. It would also be very useful to look at section 9.5.5 to understand how the different data messages work. Experimenting with ANTwareII and a pair of USB sticks is also very helpful in understanding how the protocol works.
Now, regarding to some of your specific questions:
1) Interpreting the message A4 03 40 01 4B 15 B8
In order to decode this message, refer to the serial messaging format (Section 7.1 of the ANT Message Protocol and Usage document for the basic format, and 9.5 for specific details). This particular message is CHANNEL_IN_WRONG state response to the Open Channel message.
2) If you configure your channel as receive only, acknowledged messages will not work as intended. Please configure your slave channel as a normal slave.
3) No, there is no way to stop an ANT from sending messages periodically. Bidirectional communication is still possible. The Youtube presentation covers all of these in detail.
