I had a similar error.
Some one helped me out with this and it worked for me
"Try using devmenu_2x.cia (do NOT use any other version!), I've had a lot of good luck with it. Go to the updates folder and import all cia's with L + R + A. Wait a good while for it to finish.
Then immediately, don't forget this, go to *0004013800000002.cia and select Start + Y to finish the native firm installation.
*It will be 0004013820000002.cia on new3ds.
DON'T FORGET to verify the downgraded emunand in OTPhelper before you go ahead and copy it to sysnand."
There are maybe some numbers different because your 3ds is not european.