It seems that it has to do with the age of the laptop (10-11 y/o) and perhaps the new 18.04 Ubuntu base. Because I tried with a Linux Mint 19 live usb and I had the same error message, while the laptop has Linux Lite 3.8 installed properly. So I must have installed LL 3.0 by usb when it came out. I also had Elementary installed last year or something.
And yes I've been making the usbs in the linux laptop just to be sure.
I don't really care about this laptop, I just wanted to upgrade for the sake of it. I don't mind if it stays with 3.8.
edit: I'm probably right regarding the base distro on 16.04 and 18.04. I tried with LL 3.8 and it booted in the live distro just fine. So perhaps they changed something in the 18.04 version.