No Root file system is defined
 

I have tried to install Ubuntu 11.4 on an external hard drive and it comes up with 'NO ROOT FILE SYSTEM IS DEFINED Please correct this from the partitioning menu.'

How do I do that?

Usually the installer program guesses correctly. In your case I can't be sure it did. My guess is either one of two things. One is you didn't assign / as root or the boot loader (after reboot) sees the wrong or is trying to load the wrong disk/partition.

The way you set bios and have internal disks and the way your bios works may have an impact on this type of install.

Tell us the steps that you used to do this.

Have a look through here, if you choose the advance partitioning, the 8th pic shows the root partition

http://www.linuxbsdos.com/2011/05/04...-ubuntu-11-04/

From that message it looks like GRUB is installed, and has at least started, but doesn't know where to find the root partition.

1. When you formatted the external drive did you set the partition for root as bootable?

2. When you did the install, where did it put the GRUB boot loader?