Since version 7.51 of the Datapath drivers you might run into a situation where it seems like no slides are captured even though there is a signal.
The cause is a small vertical shift in the captured image that exposes noise lines at the top of the captured image. The effects vary per resolution.
When you check the Capture tab during a recording you will notice that the motion detection grid shows a line of zero's at the top of the grid.
The effect is that motion is detect constantly and 'no motion' never occurs. So no slides can be captured.
A simple solution for this is to vertically shift the captured image. To do so open the Sources tab and select the video device defining the Datapath card.
Once selected press the Properties button. This will open the Datapath driver properties dialog.
Find the Filter Properties tab and in that tab the Vertical Position. Often it is enough to change the setting only one tick.
Remember that you can only change these settings if a source is connected to the card. Otherwise the sliders will be disabled.