When I run test panels , when Analog output is wired to analog input(channel 1 to 1), I get DC component together with sine wave. Voltage is not constant, and when changing AC output ( I hardly understand what means the scale -10,+10V on the scrollbar, for sine wave generation) the DC part changes proportionaly. I have a standard 100pin ribbon cable (unshielded). But if the DC voltage is not constant it's hard for me to believe it might be the cable cause.
Have you tried shorting ai0 to aignd and reading ai0 in RSE mode? This should result in a reading of 0 V. If the voltage is pretty different than the expected, then it could be that your board is in need of calibration.