Hi Sshenoy,
I can't run your code on my system so it's difficult to see exactly what is happening. After pressing the stop button do you wait a few seconds? Depending on what part of your code is being executed it might take some time to get to where the stop button is evaluated. You can try running your application in highlight execution to see if your application is getting stuck executing a certain VI and never making it to where your block diagram evaluates the stop button.
As well, it might help to change the mechanical action of your button. You want to make sure that the button is still pressed when your application reaches your stop logic. Right-click on your stop button on the front panel to change the mechanical action from Latch to Switch.
I hope this helps!
Emily C
Applications Engineer
National Instruments
