overwrite digital output buffer error -200292

In another attempt to generate a software timed PWM signal using cDAQ-9184 and a 9401 module I ran across another error. (I'm developing this for another application where I need 30 PWM signals, so using counters isn't practical).

I created a 1000 element buffer and am generating 1000 samples per second. I set the task to "Allow Regeneration" and set the write position to "First Sample" and Offset = 0. I then start the task. As long as I don't try to write any more samples, the proper PWM signal is continuously generated. When I try to overwrite the 1000 sample buffer with a new array, I get error -200292. 

Is there a way I can avoid this error? I have the problematic VI attached. 

Thanks,

Douwe