I had the exact same symptoms occur when I attempted to install grub to the boot block of the root partition on a dual SATA system. When allowing the installer to write grub to the MBR (sda), the install completed successfully . In that regard, your situation may be entirely different. Hard to say without more details. I saw the same behavior with both Gutsy 32 and 64 Live CDs, as well as Daryna.. Strangely, the workaround I found was to click the "advanced" button in the last installer dialog, and enter the partition for the grub installation in standard linux notation (/dev/sdXX) not the Grub syntax (HDx,x). I have no idea why this works, other than there is a bug in the ubiquity grub scripts.
I don't know if this will make any difference in your case or not, but it's a fairly simple thing to check out.