cannot install 18.04 - magic number / load kernel error

[pabc]

As the title really. I can get to the grub screen but when I select to install I get invalid magic number and need to load the kernel first.

So what I've tried....

turn off secure boot in bios and allow legacy
checked MD5sum of the iso download. all good.
Tried 3 different thumbdrives.
created the bootable disk with dd, startup disk creator, unetbootin (both linux and win7)

All fail.

Suggestions?

[pabc]

what are the odds - 4th thumbdrive and it worked fine. My fault for buying cheap generics off amazon