Further to this, if I attempt to read channel 5 it returns error value 16 (invalid channel).

Why does it recognise channel 5 as invalid, yet cause such a serious crash if I attempt to read channel 8?

Many years ago I posted on here about issues with the pt104 drivers for the RS232 Pico unit and problem accessing channel 8 (this is for a dual-input device plugged into socket 4). The problem was eventually resolved, although I found a fix for myself by reverse engineering the DLL. Now using usbpt1...