Hello Krishna,
This is indeed peculiar but I am positive is has to do with something different than the minimizing. Try to run the shipping example
"Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi" and see if your outputs are updated. Probably the rate is too fast for the machine to update the buffer but lets start here.
The other good idea, if the previous example worked, is to strip portions of the code until you can have one single Vi that reproduces the issue, then you can post it here and try to reproduce it with variations of the driver (or OSs).
Hope this helps,
Gerardo O.
RF SW Engineering R&D
National Instruments