In order for your COBRA Firing System to work correctly, the firmware version on your 18R2 must match the firmware on your firing modules and other COBRA equipment like the Audio Box.
One thing to note is that some products will have different iterations of firmware but still work together. For example, the COBRA 18R2 controller runs version 5.0.5 and the 18M firing module runs 5.0.2. This is because there were bug fixes or small changes that were only required on one device but the main firmware version is still the same at 5.0.X.
Please see below for a chart that outlines firmware compatibility.