6259 digital waveform generation issue

[Sid7117]

Hi,
I would like to generate digital waveforms on some digital lines of my USB 6259 mass termination module.Since digital waveform generation reguires
an external clock source, i've created a counter (Ctr0) task with frequency 1000.ctr0internaloutput is given as the clock source of digital output task and
rate given was 500. The data to be written to the output is saved in a TDMS FILE.My digital output loop runs at a rate of 200ms so each time it reads 200ms
of data from the file, converts it to digital waveform and writes to the output. Im getting a digital waveform in an irregular manner when i checked the
output. The waveform that im expecting at the output must be on at 3rd second and must be off at 3.5sec but i'm getting a different waveform(Pls see attached image).
If i'm generating a sequence which turns on at 2 and turns off at 3, i would get a proper waveform. Whenever i use fractions of seconds this problem arises.
What should i do to det a proper waveform?