One reason you could receive the unknown device error (-10401) is because LabVIEW obtains all of its hardware handles when it first launches. Therefore if your device was not present or completely installed the instant LabVIEW obtained the handles to the hardware it would return an error. In the case of the PCI devices, it is possible to boot LabVIEW before Measurement and Automation has finished installing the device. Similarly, any USB device installed after LabVIEW has been opened will not be represented in LabVIEW.
All you have to do to correct this problem is close your program, exit LabVIEW, and relaunch LabVIEW after the hardware has been completely installed.
You may also want to ensure that you are using DAQmx and that your device number in MAX matches
up with what you chose in LabVIEW.
Hope this helps,
AnujD.