Custom firmware .px4 file reports no end flag when uploading

I was trying to add IR Lock precision landing on my quadcopter and I followed [http://dev.ardupilot.com/wiki/building-px4-with-make/](url) to make the .px4 file after I modified the APM_Config.h file to enable precise landing and build from master branch of ardupilot as suggested by this page, [https://irlock.readme.io/docs/download-links](url). However, it keeps giving me an error like this:

> The hex file does no contain an end flag

And then followed by:

> Failed to read firmware.hex: No end flag in file

Is there anything that needs modified in Utilities/Firmware.cs or it is rooted somewhere else?

Start with Utilities/Firmware.cs and trace how Mission Planner reads the custom .px4 or firmware.hex file during upload. Reproduce the reported “No end flag in file” error using the firmware built after enabling precise landing, then determine whether the failure is in file handling or the generated firmware format; done means the cause and expected upload behavior are established.

Written by the indexing model from the issue text.