Elementary os fatal error extracting grub

leepton

Hi , is all day that im trying to install elementary os on a external disk connected to usb .

i have 1 usb memory of 14 gb with elementaryos-5.0-stable.20181016.iso downloaded from original site.

i tried to mount the iso with MBR and GPT partitons same result

so i checked my bios like no fast boot , and no secure bot.

starting the PC pressing F11 in my case , selecting the usb with the iso.

loading elemetary live

select install ok

select to install in other ..

creating the partition for external disk formatted in NFTS

frist attemp:

primary , beginning ext4 with the root / with slash
primary , beginning ext4 with the root /home

select to install on the external disk

got critical error when extrating the grub 2 during the installation

also tryed to install the swap memory like this

second attemp:

logical , end swap partiton
primary , beginning ext4 with the root / with slash

select to install on the external disk

got critical error when extrating the grub 2 during the installation

please i need a really easy to understand guide step by step