Hi everyone !

Firstly, sorry for my English, it's not my mother language by far

I'm trying to install BT5 on my 1TB external hard drive. I'm on a mac so booting OS other than MacOS/Windows is rather difficult...

Currently : this is what's on my HD : link

sdc1 is an EFI partition containing grub so that I can boot on my Mac (without it it would be impossible).
sdc2 is where Ubuntu is installed.
sdc3 is a SWAP space.
sdc3 is my Mac backup partition.

I tried to install backtrack in 100GB of the free space left, but I always had an error "Impossible to install GRUB in /dev/sdb" so I did not install the amorcer ("amorceur" in french). Even when backtrack was installed, I tried to repair the boot with boot-repair (as I did with Ubuntu), but the partition was not recognized. In fact, in Ubuntu, the partition where Backtrack was installed was shown as free space, but when I was on the backtrack live CD, files were well installed in the partition...

How can I install ? Could the order of the partition be responsible of this ?

Thanks in advance!