1st msg: To clarify a misconception for other readers as well. There is only one package called Obarun-Install, whether on live or installed system. There is no other installer. Once you start it is asks to be checked against the obarun git which has the latest to the minute version of the installer. This may actually be newer than what is in the iso or in the repository if the changes haven't made it that far. So once you update you have the same installer with eveyone else, at that moment.
2nd msg: It seems as there is something wrong with the mounted partition. Is this vm, hd, or usb/ssd disk?
Use blkid and df to see what is mounted and what format they have.
# blkid
# df
% sudo df
If it does show like a sufficient space partition that is ext4 do a check on that partition (if you are on JWM use gparted) or fsck if you are on console.
If /dev/sda1 is not mounted, the /mnt directory exists within the live system and can not be used for installation.
# mount /dev/sda1 /mnt
# ls -al /mnt
you should see one file in there, <lost-n-found> if it is ext4.