@Daniel Richter
Hi; many thanks for your answer.
No, I have no error message when launching Grub customizer. Yet if I try to close it without having made any change, it says that I should save my modifications before exiting. If then I choose to save and exit, I get a crash message for Grub customizer. (I chose to send a report but maybe you would details here? If yes which details?, I'm not too much experienced in this.) But if I save, then exit, as I always do usually, there is no crash.

To my opinion the problem started when udating Linux to 3.16.0-51; it was 3.16.0-50 before; files dates are relevant about that.

Please do ask for some more details if you need.

Thanks again for your involvment.

My /boot/grub/grub.cfg.new:

BEGIN----------------------- /boot/grub/grub.cfg.new ----------------------------

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
if [ "${next_entry}" ] ; then
   set default="${next_entry}"
   set next_entry=
   save_env next_entry
   set boot_once=true
else
   set default="0"
fi

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}
function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}
function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

if [ x$feature_default_font_path = xy ] ; then
   font=unicode
else
insmod part_msdos
insmod ext2
set root='hd0,msdos3'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos3 --hint-efi=hd0,msdos3 --hint-baremetal=ahci0,msdos3  cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d
else
  search --no-floppy --fs-uuid --set=root cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d
fi
    font="/usr/share/grub/unicode.pf2"
fi

if loadfont $font ; then
  set gfxmode=1600x900
  load_video
  insmod gfxterm
  set locale_dir=$prefix/locale
  set lang=fr_FR
  insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ] ; then
  set timeout=30
else
  if [ x$feature_timeout_style = xy ] ; then
    set timeout_style=menu
    set timeout=3
  # Fallback normal timeout code in case the timeout_style feature is
  # unavailable.
  else
    set timeout=3
  fi
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
insmod part_msdos
insmod ext2
set root='hd0,msdos6'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos6 --hint-efi=hd0,msdos6 --hint-baremetal=ahci0,msdos6  17538095-0531-414b-ba53-5f4366d4afc4
else
  search --no-floppy --fs-uuid --set=root 17538095-0531-414b-ba53-5f4366d4afc4
fi
insmod png
if background_image /luc/Images/Arrière-plans/Batal_mars_2015_1600x900.png; then
  set color_normal=light-gray/black
  set color_highlight=magenta/black
else
  set menu_color_normal=white/black
  set menu_color_highlight=black/light-gray
fi
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/09_lowlatency_proxy ###
function gfxmode {
	set gfxpayload="${1}"
	if [ "${1}" = "keep" ]; then
		set vt_handoff=vt.handoff=7
	else
		set vt_handoff=
	fi
}
if [ "${recordfail}" != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then
    if hwmatch ${prefix}/gfxblacklist.txt 3; then
      if [ ${match} = 0 ]; then
        set linux_gfx_mode=keep
      else
        set linux_gfx_mode=text
      fi
    else
      set linux_gfx_mode=text
    fi
  else
    set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode

### END /etc/grub.d/09_lowlatency_proxy ###

### BEGIN /etc/grub.d/10_linux_proxy ###
menuentry "Ubuntu, avec Linux 3.16.0-51-generic" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-51-generic-advanced-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-51-generic…'
		linux	/vmlinuz-3.16.0-51-generic root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro  quiet splash $vt_handoff
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-51-generic
}
menuentry "Ubuntu, avec Linux 3.16.0-51-lowlatency" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-51-lowlatency-advanced-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-51-lowlatency…'
		linux	/vmlinuz-3.16.0-51-lowlatency root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro  quiet splash $vt_handoff
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-51-lowlatency
}
### END /etc/grub.d/10_linux_proxy ###

### BEGIN /etc/grub.d/30_os-prober_proxy ###
set timeout_style=menu
if [ "${timeout}" = 0 ]; then
  set timeout=10
fi
### END /etc/grub.d/30_os-prober_proxy ###

### BEGIN /etc/grub.d/41_linux_proxy ###
submenu "Autres"{
menuentry "Live Ubuntu studio"{
	set root='(hd1,3)'
	search --no-floppy --fs-uuid --set 93BC-841E
	drivemap -s (hd0) ${root}
	chainloader +1
}
menuentry "Ubuntu, with Linux 3.16.0-51-generic (recovery mode)" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-51-generic-recovery-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-51-generic…'
		linux	/vmlinuz-3.16.0-51-generic root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro recovery nomodeset 
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-51-generic
}
menuentry "Ubuntu, with Linux 3.16.0-51-lowlatency (recovery mode)" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-51-lowlatency-recovery-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-51-lowlatency…'
		linux	/vmlinuz-3.16.0-51-lowlatency root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro recovery nomodeset 
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-51-lowlatency
}
menuentry "Ubuntu, avec Linux 3.16.0-50-generic" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-50-generic-advanced-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-50-generic…'
		linux	/vmlinuz-3.16.0-50-generic root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro  quiet splash $vt_handoff
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-50-generic
}
menuentry "Ubuntu, avec Linux 3.16.0-50-lowlatency" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-50-lowlatency-advanced-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-50-lowlatency…'
		linux	/vmlinuz-3.16.0-50-lowlatency root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro  quiet splash $vt_handoff
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-50-lowlatency
}
function gfxmode {
	set gfxpayload="${1}"
	if [ "${1}" = "keep" ]; then
		set vt_handoff=vt.handoff=7
	else
		set vt_handoff=
	fi
}
if [ "${recordfail}" != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then
    if hwmatch ${prefix}/gfxblacklist.txt 3; then
      if [ ${match} = 0 ]; then
        set linux_gfx_mode=keep
      else
        set linux_gfx_mode=text
      fi
    else
      set linux_gfx_mode=text
    fi
  else
    set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode

menuentry "Ubuntu, with Linux 3.16.0-50-generic (recovery mode)" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-50-generic-recovery-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-50-generic…'
		linux	/vmlinuz-3.16.0-50-generic root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro recovery nomodeset 
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-50-generic
}
menuentry "Ubuntu, with Linux 3.16.0-50-lowlatency (recovery mode)" --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.16.0-50-lowlatency-recovery-cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d' {
		recordfail
		load_video
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd1,msdos2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
		else
		  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
		fi
		echo	'Chargement de Linux 3.16.0-50-lowlatency…'
		linux	/vmlinuz-3.16.0-50-lowlatency root=UUID=cc6a03fa-bfe1-4493-9e1d-1aeb753e7d5d ro recovery nomodeset 
		echo	'Chargement du disque mémoire initial…'
		initrd	/initrd.img-3.16.0-50-lowlatency
}
menuentry "Test mémoire (memtest86+)" {
	insmod part_msdos
	insmod ext2
	set root='hd1,msdos2'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
	else
	  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
	fi
	echo	'Test mémoire…'
	knetbsd	/memtest86+.elf
}
menuentry "Test mémoire (memtest86+, console série 115200)" {
	insmod part_msdos
	insmod ext2
	set root='hd1,msdos2'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos2 --hint-efi=hd1,msdos2 --hint-baremetal=ahci1,msdos2  f285ff88-4e6e-43b9-bee2-232cb82e6652
	else
	  search --no-floppy --fs-uuid --set=root f285ff88-4e6e-43b9-bee2-232cb82e6652
	fi
	echo	'Test mémoire, serial console…'
	linux16	/memtest86+.bin console=ttyS0,115200n8
}
menuentry "Boulot (nécessite clé BitLocker)"{
	set root='(hd0,1)'
	search --no-floppy --fs-uuid --set 68C01953C01928B8
	drivemap -s (hd0) ${root}
	chainloader +1
}
}
### END /etc/grub.d/41_linux_proxy ###

### BEGIN /etc/grub.d/42_linux_xen ###

### END /etc/grub.d/42_linux_xen ###

### BEGIN /etc/grub.d/43_memtest86+_proxy ###
### END /etc/grub.d/43_memtest86+_proxy ###

### BEGIN /etc/grub.d/44_uefi-firmware ###
### END /etc/grub.d/44_uefi-firmware ###

### BEGIN /etc/grub.d/45_custom_proxy ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/45_custom_proxy ###

### BEGIN /etc/grub.d/46_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/46_custom ###

END------------------------- /boot/grub/grub.cfg.new ----------------------------