Grub consol "not seeing hd" partitions

[Grizzly]

Hi All

I have a query re Grub consol, I'm trying to prepare an erxternal USB for an 
(EFI) Mac, to do so requires mounting the installed USB from the grub consol 
(of a liveUSB)

1) I can't get to the grub consol of the live USB, shift brings the choose 
language menu and "C" does nothing

2) So I installed the same version on a lappy top as the only system and can 
get to grub from there (Shift then "C") but then grub can only see the disk 
(HD1) not the partitions (HD1, gpt1), (HD1,gpt2) etc

3) If I let either installed system or LiveUSB run up I can then see the 
partitions on sdb (sdb1, sdb2 etc) then

Any pointers please

P.S. I can't do this on the mac as the owner has  (with good reason**) quarm's 
about having Ubuntu make "A N Y" changes to the mac

**Last time we tried from the mac

1) Mac have changed their file system, and at the moment cloaning software that 
would have made a backup to return to no longer works

2) Mac could ONLY boot if external USB was connected

3) many tests later mac again boots but now ubuntu cant (not even seen in 
option screen)