There was a bug in X-series board NI-DAQmx driver, versions 9.4 and earlier, which caused the MainProtocol to stop after 1hr, 29min.  We have tested the new NI-DAQmx 9.5 driver, and the BUG HAS BEEN FIXED.

Now the X-series boards are as good, or better than the equivalent M-series boards.  If you are considering buying the PCIexpress bus equivalent of the venerable PCI bus M-series PCI-6221 board, this new PCIexpress X-series PCIe-6321 board now works fine (provided you install the NI-DAQmx 9.5 driver). 

To download and install the latest NI-DAQmx driver, go here.