If there's not enough space on the target drive and the user chooses to go back and fix the package selections a bit, the installer does not unmount /tmp/hdimage as it probably should. Currently, the user has to unmount it before proceeding to package installation, otherwise the installer reports the device as busy and cannot continue.
Please verify with 6.0
just hitting retry should work. *** This bug has been marked as a duplicate of 2700 ***