Wrong pulse counting for tick based pulse generation for USB6210

I try to  generate 50 HZ pulse in USB 6210 with sample code "http://zone.ni.com/devzone/cda/epd/p/id/3088". But doesn't work properly.

Please see attachment:

app.jpg: pluses setting. I set 200000 ticks to low and high.

Tick count based.jpg : result wave  from oscilloscope.

You will see low is 3 times longer than and high.

Do you have any idea?

Thanks.