Hello Gurupreet,
You can't start a clocked analog output with nothing in the buffer. You need to use a DAQmx Write VI to put samples in the buffer before you use the DAQmx Start VI. You should check out some of the examples in the Example Finder under Hardware Input and Output>DAQmx>Analog Output for guidance on setting up a buffered, timed analog output channel.
It's not clear from your code, but I'm guessing that you probably want to write your entire output array to the AO buffer and use regeneration to send the buffer continuously while acquiring some response at the same time. If this is the case you probably also want to synchronize your input to your output through the use of some sort of triggering on the analog input. If you do this you should also use your error wires to force the AI task to start before the AO task to prevent a race condition. A good example of this can be found here.
