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Please note that inactive accounts are deleted at regular times. If you create a new account, you must be logged into Battle.net long enough (either in one session, or spread over several) to have accumulated 2 hours of time within the first 48 hours. After that, your account becomes permanent so long as you continue to log into this account once every three months.

It can also be possible that the server you are connecting to has been split from the network and has not received your new account information if the account was recently created.