Instead of using the front slot (that's for thick, stiffer media) use either the main sheet slot on top. Museo recommends this on their "museo pan paper set-up' pdf or use the "Single Sheet" slot. It's on top behind the main sheet slot. Install the "Feeder" at the back if you haven't already.
The deal with this rear slot is learning how to apply the right amount of pressure to the sheet as you get it to grab. Finicky enough with !9 inch paper. With 40 inch I imagine trickier.
Hope that helps
Cheers,
Doug