Greetings,
The NI 6514 is only supported under the new NI-DAQmx driver. ReadFromDigitalLine is a function provided by the Traditional NI-DAQ driver. Thus, you will be unable to use it with the NI 6514. I would suggest that you examine the ReadDigChan.prj example. It demonstrates how to read from one of the NI 6514's digital lines with NI-DAQmx. It is available in the following location:
C:\Program Files\National Instruments\CVI70\samples\DAQmx\Digital\Read Values\Read Dig Chan
Good luck with your application.
Spencer S.