When I enter a new account name, I get “[LE-51] An unknown error occurred.” I tried several different account names and rebooting, no effect.
This exact situation happened to me as well, and it is quite frustrating as I have two friends who own the game and are able to play with no issue, but I am unable to get past this error.
I was eventually able to sign in by using a different name. Both names were the same length and capital and lowercase letters, no numbers or symbols, and I think the first name was unique enough that no one would’ve taken it first. So I’m not sure what’s going on here.