ID 1 is for F interference sniffing. Set the MRF300 to ID1. This is done on the bottom of the MRF unit. Slide the cover back and you will see the dial.
In the MX3000 software, at the top of the window you should see a little antenna. Click on the antenna. A window should pop up and at the bottom you should see where you can change the ID. Change it to ID 1. Then it should work.