I'll try again if they servers are not busy.. because some say that if it was really bricked, powersaves wouldn't read it. In my case. powersaves can read it well. The only issues is when I try to apply some code, then that error show up.
It's bricked. Same exact thing happened to me. I even tried using powersaves on a different computer and used the cartridge on a different 3DS and yeah the 3DS would never read it. Powersaves was the only thing that read the cartridge and it let me restore backups but everytime I tried applying a code it would throw out that same error. No matter how many backups or whatever backup I restored neither 3DS would read it