While it's true that the installation would have failed later due to the problem Carthik points out, this looks like a different bug to me; the traceback is quite different.
** This bug is no longer a duplicate of bug 47046 breaks if system partitions are not reformatted -- Partition problems + Installer chased https://launchpad.net/bugs/51077 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
