Attempting to install UCS 4.1 on a Beelink Z83 II, I'm experiencing a similar issue to the one described in Bug 39009. I'm getting this:
Booting in insecure mode
error: variable `prefix´ isn´t set.
Loading step 1
...and then a grub prompt.
I have tried a couple of workarounds mentioned in Bug 39009:
I have removed /efi/boot from the ISO. This didn't work because the Beelink Z83 II does not support legacy boot mode. There is no way to disable UEFI.
I have tried installing UCS_3.2-4-UEFI-amd64.iso. The Beelink Z83 II will not boot from a USB key with this ISO; it behaves the same as when booting from the 4.1 ISO without /efi/boot (ignores the USB key and attempts to boot from the hard drive).
I'd really appreciate any help with this. I'm trying to replace a Zentyal box because UCS is so much better.