Sorry, I no longer have LabVIEW 7.1, and I also don't have your hardware, so I will not be able to reproduce your claimed problem.
Overall, the program is quite nice for a beginner, but I have a few points you might look into at your leisure:
As said, most likely none of this is in any way related to the problem you are observing. They are just a few quick ideas to improve dataflow and code readability. Good luck! 🙂