Resulting error: the requested subsystem 'analog input' does not exist on this device in Session-based Interface using an NI SCXI-1520

I am using a session-based interface for 64-bit version with DAQ toolbox 3.1. I am attempting to interface Matlab with an NI SCXI-1000 to USB-6251 mass termination device. The issue is trying to add channels. Through NI DAQmx 14.0, it will add 'Dev1', but not 'SC1Mod1', 'SC1Mod2', or 'SC1Mod3'. Matlab recognizes it is connected, but will not add the channel. It results in "the requested subsystem 'analog input' does not exist on this device." Any ideas why?

Thanks, Greg