The error -200284 usually occurs when the timing parameters are not set correctly. This is thoroughly explained in the KnowledgeBase Article: Why Do I Get Error -200284 When I Set a Small Sampling Rate in DAQmx? However, when I set up and run a modified version of the acquireNScans.c example to match you parameters on a USB-6009, I do not receive any errors. Try running the attached file to see if you get the same error.
You mention that you use a button to start the acquisition. How are you handling a button press event? If the problem persists, please post a larger picture of your application to better show possible causes.