PreArm : "Param Storage Failed" error occured

Hello,
I’m using arducopter with Pixhawk2 (Orange Cube).

My drone sometimes does not arm its motor again, after landing.
On the Mission Planner, there is a message “Param Storage Failed”.
I have to reboot pixhawk to fly again.
The error message does not appear after every landing, but once shown up, there is no way to arming again with out reboot Pixhawk.

I’m trying to test my multicopter with my modified S/W.
My S/W is based on Copter 4.0.7.
My s/w is modified many times and the error appears after recent modification.
I modified “Land detector” and “config.h”.

In the “land detector”, I changed some criteria of judging land or not.
In the “config.h”, I changed value of ‘LAND_DETECTOR_ACCEL_MAX’, 1.0 to 3.0.