Hello Herve:
In that blog Erich recommends to set the FSEC byte (not bit) to 0xFE. As you can see in the same blog, you have to set this in the Flash Configuration Field value as showed with the pictures.
- For a project with PEx + KSDK: You will find this configuration in the file startup_MK64F12.S:

- For a project with only PEx: You can disable code generation for the CPU component (right click on component -> Code Generation -> Don't Write Generated Component Modules) and changing the FSEC field in CPU_Config.h:

Regards!,
Jorge Gonzalez
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