Did you get an answer from somewhere?
I had the same problem, and I think (after 3 or 4 re-failed re-installs),
I have the depressing answer -- this version does not support ext4 install.
It will format a disk partition using ext4, but then fails with the above error.
No other indication anything is "wrong", nor could I find a note to that effect.
But there was a reference to this limitation in another posting.