grub2 não inicializando o linux

Question

Meu computador tem

Disco rígido SATA interno (/ dev / sda) que possui o linuxmint-13.

/dev/sda1 = linuxmint-13
/dev/sda2 = extended partition
/dev/sda5 = swap

HDD USB Externo (/ dev / sdb) que possui o linuxmint-17.

/dev/sdb1 = linuxmint-17
/dev/sdb2 = extended partition
/dev/sdb5 = swap
/dev/sdb6 = linuxfromscratch
/dev/sdb7 = formatted partition but blank

Ao selecionar boot a partir do drive usb (/ dev / sdb), o menu grub2 (on / dev / sdb) mostra

linuxmint-13
linuxmint-17
memtest
linuxfromscratch

linuxmint-13, linuxmint-17 e memtest funcionam corretamente

Ao selecionar linuxfromscratch, uma mensagem de erro "no such device with uuid" aparece e ao retornar, o menu grub2 reaparece

A parte relevante no grub.cfg

menuentry 'Linux From Scratch (7.7) (on /dev/sdb6)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-2374b32b-3453-58fe-feaf-317821aa67f9' {  
    insmod part_msdos  
    insmod ext2  
    set root='hd1,msdos6'  
    if [ x$feature_platform_search_hint = xy ]; then  
      search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos6 --hint-efi=hd1,msdos6 --hint-baremetal=ahci1,msdos6  2374b32b-3453-58fe-feaf-317821aa67f9  
    else  
      search --no-floppy --fs-uuid --set=root 2374b32b-3453-58fe-feaf-317821aa67f9  
    fi  
    linux /boot/vmlinuz-3.19-lfs-7.7 root=/dev/sdb6 ro  
}  
submenu 'Advanced options for Linux From Scratch (7.7) (on /dev/sdb6)' $menuentry_id_option 'osprober-gnulinux-advanced-2374b32b-3453-58fe-feaf-317821aa67f9' {  
    menuentry 'GNU/Linux, Linux 3.19-lfs-7.7 (on /dev/sdb6)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-3.19-lfs-7.7--2374b32b-3453-58fe-feaf-317821aa67f9' {  
        insmod part_msdos  
        insmod ext2  
        set root='hd1,msdos6'  
        if [ x$feature_platform_search_hint = xy ]; then  
          search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos6 --hint-efi=hd1,msdos6 --hint-baremetal=ahci1,msdos6  2374b32b-3453-58fe-feaf-317821aa67f9  
        else  
          search --no-floppy --fs-uuid --set=root 2374b32b-3453-58fe-feaf-317821aa67f9  
        fi  
        linux /boot/vmlinuz-3.19-lfs-7.7 root=/dev/sdb6 ro  
    }  
}  


$ blkid /dev/sdb6  
/dev/sdb6: UUID="2374b32b-3453-58fe-feaf-317821aa67f9" TYPE="ext4"  

Nota: os uuids são exemplos (mas, como os exemplos aqui, blkid e grub.cfg têm uuids correspondentes)

Por favor ajude.