I'm a bit confused by what you say you are doing. I think you could wind up with an error on your analog input acquisition as the buffer overwrites. You will acquire 1000 samples on a single pass through the outer while loop. The buffers will continue to acquire data after that. You pass your 1000 points through a couple of add operations and onto the analog output. I don't think you need the DAQmx task start VI as you told it to autostart when you wrote the data to it. It should be sending data continuously.
But you trap the operation of the outer while loop by way of the inner while loop where you wait for an error or the Stop button to be pressed. The input buffers of the analog input task I'm sure will fill up in that time. So once those wavform indicators get their first set of data, they won't see any new data until you press the stop button.
Don't use a False wired to the outer while loop's stop terminal. You have no way of stopping the program gracefully. You will be forced to abort it. And the inner while loops with a True wired to their stop terminals serve no purpose as they will just execute the one time.
