Digital I/O problem for NI USB-6008

I want to use digital lines from NI USB-6008 DAQ device using the session-based interface and the Data Acquisition Toolbox. I can see all analog and digital I/O using NI MAX program. When I run daq.getDevices it only displays the AnalogInput, AnalogOutput, and Counter channels. And when I use addDigitalChannel command I received the following error:

No appropriate method, property, or field addDigitalChannel for class daq.ni.Session.

Please, can you help me to use digital I/O of my NI USB-6008 DAQ device?