The 18R2, 36M, 72M, and the Audio Box utilizes two pieces of firmware, one for the processor, which loads via the USB port, and one for the transceiver which loads via the Wireless Re-programmer. Er6 means these two firmware versions are mismatched.
When upgrading the 18R2, it's normal for the unit to display Er6 after the transceiver is updated. If this occurs, please proceed to the next step, which is loading the cobra.s19 file using the USB drive. If you are using the COBRA Reprogramming Software and have closed the program or are no longer on the correct step to updating your device, you can start over by selecting to update your 18R2. The software will walk you through the proper steps, eventually bringing you to the stage where you load the cobra.s19 file. Once this is complete, Er6 will disappear, and the correct firmware will display on the unit during the startup process.