The big problem is in your Stop Acquistion event. You are executing the LabVIEW stop sign which is the equivalent of hitting the abort button on the toolbar. (Check the context help on that.) You may want to stop the acquisition, but you don't want to stop your LabVIEW program. You need that event case to transition your state machine into an idle mode where you aren't doing any acquistion. Then hitting the start acquisition button again transitions the state machine back into acquiring.
Similarly in your Exit program event, you don't want to actually exit LabVIEW there. You want to execute any shutdown commands such as closing the com port and any of those activeX references. Then allow that to stop the while loop. PUt the Exit LabVIEW function outside of the loop so that once everything is cleaned up, your application can exit. You will probably want to wrap that command up in a case structure so that if you are in the run-time enviroment, it will exit your application. But if you are in the development environment, you don't want to cause your entire LabVIEW environment to shut down. One other thing is that right now you actually have a race condition in the Exit event. Will the com port close first or will LabVIEW exit. There is no defined order of execution.
You may also want to have an event for the Panel Close? that way you don't accidentally short circuit your entire program by hitting the X button. You want to catch that event, discard it. And if you do want to actually shut down, have it trigger the Exit Program button so that you can gracefully shutdown.
