Hi Bob,
Thanks for posting on the NI Discussion Forums! Unfortunately, you cannot use LabWindows CVI 6.0 to access a PXI-6221 device. The reason being is that this device falls under our M-series device family. These device can only be programmed with NI-DAQmx. The earliest version of LabWindows CVI that is compatible with NI-DAQmx is LabWindows CVI 7.0. Your only options are to either upgrade LabWindows CVI, or use a device which can be programmed using our Traditional Daq legacy driver. Let me know if you have any additional questions/concerns.
Rod T.
