Steve,
The error you are getting is because you cannot scan the same channel multiple times in the same scan list. I do see why you would want to do this though. You may want to add a "start-up" routine where you have a sequence structure that acquires on a certain channel with a different gain each sequence and picks the best one. As far as adding the same channel to the same scan list with different gains, that will cause the error you are seeing.
Ross C
National Instruments
