Any idea which SparkMax it could be? From the error message or some other log? Why are you guessing negative kI? If it is closed loop related that narrows it down for me. I only have 3 doing closed loop processing. I will look tomorrow.
I think there are three cases:
1/ Your NEO motor controllers are not connected to the robot
2/ You have not updated the motor controllers firmware/ set their IDs
3/ You set the motor ids incorrectly
If you are not setting negative kI, check the PID values you are setting. We had some problems where the PID values wanted to be doubles, but we were putting in integers, so we got an error (ex. P being set to 0 instead of 0.0)