Hi,

I've just verified this for the most recent build of grml64-small (being
https://jenkins.grml.org/job/grml64-small_sid/881/artifact/grml_isos/ as of
now), works as expected with grml2usb 0.14.4 (verified the result via
"qemu-system-x86_64 -bios /usr/share/ovmf/OVMF.fd [...]"). This is a problem of
the 2014.03 ISOs (which I just verified, got the same error message as you)
which lack the bug fix for UEFI boot which is included in recent grml-live
versions
(https://github.com/grml/grml-live/commit/8d91fa8e1b3b6d46a1333928a7384a463868cce0),
so all the new Grml builds should be working just fine.

regards,
-mika-