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.
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.