Trying to install 6.0 from hard disk, with the dist sitting on a filesystem which is regularly mounted as /u2 in my fstab, the install failed while trying to mount all the filesystems listed in my fstab. The error was (approx): "device is already mounted -- using symlink", followed by "file or directory exists". It then unmounted everything and gave up. It presented a re-try button which incidentally did nothing worthwhile at all, since it didn't even try to re-mount the filesystems that had been unmounted after the error, but that should be a separate bug if at all. I worked around this fairly easily by removing the filesystem containing the 6.0 dist from my fstab and restarting the install.
*** This bug has been marked as a duplicate of 2504 ***