Originally Posted by guanx
Though not very likely the problem, please mount your installation source to somewhere other than /mnt because /mnt will be used as installation destiation.
Oh, but it will most likely be the source of the OP's issue! This is what the installer tells you if you want to use a pre-mounted directory:
OK, we will install from a directory within the current
filesystem. If you have mounted this directory yourself,
you should not use /mnt or /var/log/mount as mount points,
since Setup might need to use these directories. You may
install from any part of the current directory structure,
no matter what the media is (including NFS). You will need
to type in the name of the directory containing the
subdirectories for each source disk.
Which directory would you like to install from?
If I need to mount something in the installer, I usually do a "mkdir /alien" and mount there.