Mathieu,
The flash bank on that device ends at 0x3FFFF, the export setting you have is exporting 0x3FFFF words. Therefore you are overshooting the range into undelared/mapped memory region. To export it properly, use 0xFFFF words instead.
I notice the error messages, the wording and information on that window is not as clear as it should be, these will be on our list to be improved in the next version.
Victor