If using the DLL based interface, it is important to understand how the ATI is initialized with respect to referencing account names. The ATI is initialized to the first account name used in the first calling function.
Some functions accept an account name as a parameter. In most if not all functions, these parameters can be left blank in which case the "Default" account will be used. You can set the Default account by left mouse clicking on the File menu in the NinjaTrader Control Center and selecting the menu item Options, once in the Options window select the ATI tab and select the account you want to use from the Default account menu. If your default account is set to 'Sim101' and you call functions and leave the account parameter blank, the Sim101 account will be automatically used.