After a new sub account is created, users are unable to login. When trying to generate a new password themselves, they get a warning that the account is inactive.
Current ASM release
When creating a subaccount, immediately click the "reset password" button on the right. This will automatically email a new password to the user, who should use this password when logging in. Until a user logs into an account, it will be marked as "inactive", and they will be unable to reset the password.