Hello from Australia!
I also had my Blackvue self-brick, with it booting to the Korean "upgrade failed" error message. I think it bricked after the Blackvue was powered off whilst it was still originally booting up & it corrupted itself. (I only moved my car from driveway to garage)
Thanks to your instructions I've now fixed my dashcam!!!

I had a little trouble with translations & following the instructions/process above, so below is the consolidated steps which fixed my unit...
1. Connect serial console to computer at 115200/8/N & no flow control.
2. Power on Blackvue, boot status should appear
3. Soon after powering on (or resetting), press the 'd' key to enter the boot loader config.
---Restore Root File System---
4. At the boot prompt type: loadb 0x82000000
5. Then immediately use your terminal program to KERMIT send the cramfsImage_DR500GW file from the BlackVue\System\upgrade folder within the firmware download ZIP. (I used Terra-Term, File Menu > Transfer > Send > Kermit command. It took hours!)
6. The terminal should then say that the transfer was OK
7. At the boot prompt type: nand erase 0xa00000 0xdd0000
8. Then to "write the file system of the NAND flash memory", type: nand write 0x82000000 0xa00000 0xdd0000
---Restore system software---
9. Copy patch_DR500GW.bin file to root of SD card & Reboot the Blackvue
10. Blackvue will boot up - and in my case still got stuck looping the korean 'upgrade failed' error message. Press CONTROL+C
11. Login as username = root & password = pt
12. Enter these commands... (I *think* this is what worked for me, I had some confusion with the original forum thread with these instructions; see
http://car-dvr.info/forum/index.php?topic=801.0 for clarification
# cd /
# mount -t vfat /dev/mmcblk0
# umount /mnt/nand
# /usr/sbin/flash_eraseall /dev/mtd4
# mount -t yaffs2 /dev/mtdblock4 /mnt/nand
# tar -xvzf /mnt/mmc/patch_DR500GW.bin -C /
# sync
# reboot
13. The Blackvue should then boot 'normally' again and reformat the SD card!
Hopefully that helps others out as I thought mine was dead until I found this info :D