Hi there, as for the DiskWarrior error code you met, I suggest you report it to Alsoft while trying to rebuild the directory in the lower version by putting DiskWarrior into Scavenge mode (Re-run DiskWarrior on the external HD again, press the Option key when choosing Rebuild). If the rebuilding fails, do as Disk Utility suggests: back up files, reformat your disk, and restore files. Provided that your external hard drive keeps unmounted, you cannot back up the files on it. You, therefore, should use data recovery software to access the files on it beforehand and then reformat your external HD.
Download iBoysoft Data Recovery Software to scan for inaccessible files on the external hard drive and go to format your disk.
