Hello;
The event you are trying to program is not supported by your hardware. The best way to go about that is to generate a pulse train, on the frequence you want the counter to fire, with one of the counters you have on that board of your; and to have the output of that counter routed to the gate input of one of the counters of a TIO device. The TIO devices support triggered pulse train generations.
Regards
Filipe A.
Applications Engineer
National Instruments