Format your usb device to one partition with fat32 (and GPT!) and copy all files from the iso to that.
This should look like this:
Now go to /boot/grub/ and open grub.cfg with any editor but with sudo, then replace all UUID=5c403dad00049b51 to UUID=YOUR-UUID for example in my case: UUID=56EF-38B0
You can get your UUID also with gparted, if you do a right click on the partition and click information.