Here's the answer of Dev's regarding the issue:
Why am I getting this error when starting the game/app?
Sorry for the inconvenience, but if your error code is "999666999," your account is getting that error due to a problem with its contents. Unfortunately, there isn't much we can do about that, but it may have been caused by having too many items, incorrect items, inconsistent parameters with your specific account, etc.
Because the issue is account specific, please open a new account to get access to the game again. Thank you for your understanding and cooperation.
source: Archel Betsuki Jr






